No, I haven't done any GPU work on crypto-projects.
And yes the maths are mainly EC multiplications ... but isn't the verification already offloaded to ASICs?
Also, I think that this parallel process for verifying EC signatures is what is done already for Bitshares. Maybe it's the same for Graphene as a whole and applies to Steem? I'll need to check into this ...
ASICs only do the hashing in bitcoin. Verification is still cpu-bound...
Now I know ...