He is! He's met Minako and several other members of SEES, though he hasn't heard about Minato yet.

Sensing his Personas is fine unless he's actively trying to hide them, since he's able to fool and sneak up on the party in canon, despite them having a Navi with them. He's not likely to, though, since he's already found out the Thieves know his secrets anyway.

(I haven't seen any references to Raidou in P5, but there's references to P4 characters that make it clear they're in the same setting.)