can you feel my heart?
If you're talking about whether or not it's an OHKO move and therefore not allowed by the standard clauses, Final Gambit is very clearly not an OHKO move. Nearly all users of it have moderate to low HP anyway (Staraptor, Accelgor, Shedinja). It doesn't have the level requirements of other OHKO moves like Fissure, nor does it have a 30% accuracy.
If you weren't asking about the OHKO clause, then I wonder what the purpose of this thread is.