Going by the criteria for eligibility, here are some DTM rejects:
James Thompson - One of the best touring car drivers in the world struggled in an uncompetetive Audi TT-R in 2000.
Christian Menzel - More people will remember him for his hysterical commentary of the final STW race in 1999 than for his DTM career.
Darren Turner - Wasted two years in this series. But he got better afterwards.
Peter Mamerow - Hopeless privateer effort, who just hadn't the same pace as the big budget works teams.
David Saelens - Did F3000 and DTM in a single year in 2001. After his attempts at open-wheel and touring car racing failed, his career fizzled out in the Porsche Supercup (Which seems to be a parking lot for failed race drivers...).
Yves Olivier - Who? *pause* Exactly!
Katsutomo Kaneishi - What would a race series be without a hopeless Japanese reject?
Peter Terting - He was probably way too young to be put into a DTM car. While his further career isn't worth mentioning, he's done much better on the romantic front. He's going to marry Katherine Legge! Lucky bastard, indeed.
Jeroen Bleekemolen - Drove for Opel in a time, where they didn't have the money to compete with Mercedes and Audi on equal grounds. It didn't help that he had to drive year-old-cars, too.
Rinaldo Capello* - One more proof that excellent endurance race drivers don't have to be good sprint race drivers.
Jarek Janis - Was just driving around at the back of the field in 2004, but somehow got a ChampCar drive with Dale Coyne the same year! But then again, rejects and Dale Coyne seem to fit together like Yin and Yang.
Pierre Kaffer - Same thing as with Capello. He's been way better at endurance racing that at sprint racing.
Olivier Tielemans - Racing with a team led by Colin Kolles isn't a good sign. His career fizzled out in WTCC afterwards, but I couldn't find any further info on Wikipedia.
Nicolas Kiesa - Another driver from Futurecome-TME (And don't worry, there are more to come!), whose only notable scene was his participation at the multi-car pileup at the 2006 Barcelona race.
Thed Björk - Couldn't do much in his two races as a replacement for Kiesa. But he made a good career in Swedish touring cars afterwards.
Vanina Ickx - THE ur-example of a driver placed into a cockpit, solely for marketing reasons. I mean, she is at least Jackie Ickx's daughter, what could possibly go wrong? Answer: Everything.
Mathias Lauda - A well earned induction into the DTM hall-of-shame. Judging by his performance on the track, it seemed like he only bought the rights to bear the surname "Lauda" from Niki. Well then Niki, like your failed airlines, this was another bad deal you've done here.
Susie Wolff - She's now in her 7th(!) season, yet she's still not unrejectified. And she'll probably stay in DTM for a couple of more years, as she's married to the shareholder of HWA (The company that builds the DTM cars for Mercedes) and Williams. At least she can claim to have "survived" Vanina Ickx, Katherine Legge and if she's sacked at the end of the year, Rahel Frey.
Lucas Luhr - Sadly one more wasted talent in DTM, but he got waaaaaaaaay better after his DTM career. He won the ALMS title in 2008 as well as the FIA GT1 title in 2011.
Adam Carroll - He had more success in GP2 than in DTM. But even after his DTM career, he still jumps around the many junior formula series such as AutoGP or FR3.5. Oh, and he drove for, you guessed it, Colin Kolles in 2007. Seriously, if you want to build up a good reputation as a race driver, don't drive for Colin Kolles!
Maro Engel - Several points finishes weren't enough to escape rejectification.
Katherine Legge - Maybe she should have stayed in America, because she seemed to have slightly more talent in open-wheelers than touring cars.
Johannes Seidlitz - How the hell did he get a DTM cockpit?...Oh, he raced for Colin Kolles of course! But seriously, how does a season in the Formula Renault BARC series qualify one for a DTM seat? His only memorable scene was curious crash with his team mate Bakkerud at Dijon.
Tomas Kostka - Let me quote Wikipedia here: "His performances in his national series were enough to be signed by Colin Kolles to drive a two-year-old Audi A4 for his DTM team for 2009." Yeah, right.
But to be fair, his results weren't so bad, considering that he drove a two-year-old Audi.
Christian Bakkerud - Even if he sadly died last year, he'll still be fondly remembered by DTM fans...for his rejectful 2009 season! His "highlight" was a disqualification at Zandvoort, because of a missed weight check!
David Coulthard - Yes, I didn't make this up. David Coulthard is still a DTM reject! And judging by his performance in this season so far, he'll likely stay one.
Congfu Cheng - The most blatant marketing ploy EVER by the DTM! He was placed in a cockpit, solely to have someone they could use to advertise their infamous Shanghai race from 2010. Was thankfully dropped after that season, after it became apparant that there won't be any further races in China.
Darryl O'Young - Crashed his Audi in qualifying at Shanghai, thus he could never start in his only DTM race.
Renger van der Zande - His results weren't too special, and he had the misfortune to hail from a country that wasn't considered to be "an imporant market" by Mercedes. Yes, I'm serious, that's what they told him! I repeat, Mercedes didn't consider a driver from the Netherlands to be imporant for marketing, despite the fact that THEY RACE AT ZANDVOORT FOR MORE THAN 10 YEARS NOW!
Rahel Frey - She continues the tradition of rejectful female DTM drivers, driving constantly at the back of the field, too. But hey, at least she didn't destroy any race cars!
*His fifth place in the 2004 Shanghai doesn't count, as it was a non-championship round.
