Yes combing DMT with nootropics completely changes things. You have to take in to consideration that you are activating multiple receptors with different chemicals so of course there is going to be potential for it to become not what you expected and or desired.

Mixing just never went well for apart from at very low doses of DMT and n02.

If you want a list of drugs that are safe to interact with DMT then look here: Known substance-interactions and their effects - DMT-Nexus Wiki

but safe doesn't necessarily guarantee a pleasant or desirable trip... just be aware of that.