I had to go down about 20 people on the global leaderboard, but finally did find someone with this achievement, but not the Spring 2011 ones, so might be legit. FH Poker is pretty much the only game she plays. And why would she only cheat some of the achievements but not all of them?
No one on TA has it yet, but those members likely only play the bare minimum of games until they unlock all the achievements then never touch it again.
I'll confirm for sure if it's not retroactive when I pop it since I have been keeping an exact count of my Heat hands since the DLC came out. If it pops well before I hit 2500 then it's retro, if it doesn't, then it probably is not retro. So far I am up to 844 hands played since the DLC was released.