No, Russia Isn't Helping to Build the Deep Space Gateway

At least not yet. Possibly never.

Russia's media outlets released claims Roscosmos and NASA had signed an agreement where Russia would help the US build the new Deep Space Gateway space station. 

The actual truth of the matter is that Russia and NASA signed an agreement to study how Russia might participate in the DSG.

The difference is pretty big.  

One claims the Russians are full participants.  The other, more truthful one, is along the lines of "let's talk about it."

The Russians might have aspirations for participating in deep space exploration, but to be, frank, they have slipped the delivery of their science lab for the ISS yet again.  Now it will be in 2019.  The ISS is now going on 20 years old, the Russians haven't finished their part...and they want to go into deep space?

hmmm.

To be fair, NASA keeps slipping their own missions, too. (also looking at you, JWST) However, the DSG is slated to start construction now in June 2022 with the second SLS launch.

However, given Russia's bad behavior on Earth and the lack of a need to make sure their scientists don't go off to sell their services to other countries (the pitch for why ISS instead of the SSC to Clinton), why bother with them?