Celje,
I haven't been able to find a copy of the DLS EULA (not having a copy of Trainz, I can't register on the DLS) but I'm guessing the story is something like this:
When you upload something to the DLS you transfer the intellectual property rights to Auran. You then have no rights to profit from that intellectual property, or control what is done with it, only Auran does. If a third party should profit from it, that is a matter between Auran and that 3rd party, it has nothing to do with you.
This wouldn't matter if there was no, or limited, potential to profit from that intellectual property. Also if the only way to profit from it was to sell a product, where the seller has a lot to lose by getting caught infringing others' rights. It's only become a problem because someone (happens to be Auran, but it doesn't matter who) is now offering a substantial cash prize. If you have surrendered your intellectual property rights to Auran on what you have previously uploaded then if someone wins $1,000 from Auran by doing 5 minutes' additional work on one of your previous uploads, from a legal standpoint that is Auran's loss, not yours. You can make no claim against the prizewinner. The problem of theft of intellectual property is entirely Auran's, it's completely out of your hands, even though you are the one who has suffered most from it.
As a volunteer developer I would not agree to hand over intellectual property rights for free, as a matter of principle. I also wouldn't do it on the off-chance that I might win a prize, again as a matter of principle. If I was guaranteed to receive a share of any profit made then I would have no problem with it. I naturally presumed that freelance developers whose routes etc were included in the Trainz product would receive royalty payments, but it's now dawning on me that they must be receiving nothing. From a business perspective it makes no sense to me to pay no reward to proven committed contributors, and then splash out on rewarding an individual who may have never made, or ever make in future, any other contribution to the product. Auran is doubtless visualising a flood of new session content in time for Christmas, and short-term cash-flow, whereas I'm visualising a concerned and disgruntled volunteer developer community, and the risk this presents to the long-term success of the Trainz franchise. What kind of developer community Auran wants is up to Auran, not us. We only have to decide whether to buy, and then perhaps donate or sell content for, the product.
As I see it Celje, you can half-solve this problem by publishing your work elsewhere, either on your own website (yes, people will find it), or on sites like train-sim.com where developers retain intellectual property rights. This doesn't physically prevent someone downloading your work from there and submitting it to Auran and winning a prize, but they will have violated your intellectual property rights in doing so. In practice you could only find out that this had happened after the prizemoney had been awarded, and your chances of getting that money back from the winner - who is probably in another country - would be about zero. It's not like you could claim damages from them either, because you won't have lost sales, only the prizemoney. To completely solve the problem, either sell your work so you profit from it, or don't spend your volunteer effort on things that others can exploit.