Reggie in Mario Tennis?  That doesn't sound right!  Motoi Sakuraba's team = Motoi Sakuraba for synth soundtracks, but yeah, Mr. Sakuraba hase done everything Camelot has made for generations (as well as Tri-Ace's Star Ocean series).
To be honest, I wasn't very satisfied with Mario Tennis's soundtrack on either N64 or GBC...the songs fit, but weren't memorable--like underscoring for trivial cut-scenes in a RPG.  I'm hoping this Mario Tennis game is more along the lines of Mario Golf GBC's soundtrack.  Many of those songs were upbeat enough for Tennis, but much catchier.