No, NV is a true Fallout game. Fallout 3 is more of a spinoff, except it happens to be canon because the people who made it own the franchise now and can do whatever they want.
Cute, but technically all the Fallout games except Fallout 1 and 2 are spin-offs, since their storylines are only very loosely tied to each other. I don't consider Fallout 2 a spin-off since the protagonist is a direct decendant of Fallout 1's protagonist, while characters in other games rarely share past with characters in previous games (notable mentions go to Tandi, Harold and Marcus).
The only reason I think Tactics isn't considered a full Fallout game is because of its lore conflicts. Had it been more loyal to canon, it would be a Fallout game just like the others.
And FOBOS is so much of a spin-off that it only shares a common title with the others.