No, no, some old school Megaten fans would kill you for saying such things heh. Persona is a spinoff series in the franchise. This is part of the original mainline series that's nothing like modern Persona. Atlus USA just uses "SMT" as part of its branding here.
Well I wouldn't say "nothing" like Persona since some of the Persona's are enemies you meet and collect etc in SMT games, and it has similar atmosphere in "some" parts.
It's just that the main SMT (Nocturne my favourite, still need to finish) has a much much darker atmophere than Persona games, which is nice because variety is the spice of life.
P.S SMT4 will make me buy a 3DS, can't wait.