No, DLC's on Steam can only be used for the Steam version of Trainz and if you don't own the Steam version, you can't buy the Steam DLC's.
You have two choices:
- rebuy Trainz for Steam so you can buy the DLC's there;
- buy the DLC's at the Trainz Store.
More info:
You can however use N3V DLC's in the Steam version, but not vice versa.
If you already bought a DLC there, then you'll want to contact the helpdesk so they can add the DLC to your Trainz account so you don't have to rebuy it.
Cheers
