Scout/Rogue - Spring Attack into flanking position. Skirmish plus Sneak Attack - not as punishing as a Ninja/Rogue, but he'd also get an AC bonus.
Ninja/Rogue would wind up with massive MAD - Dex, Wis, Con, Str(probably), Int(for skills, not necessarily vital, but good to have). The only one you don't really need is Cha, but then you're not as good with several handy skills (Bluff to feint, etc. Disguise, UMD).
Scout/Rogue doesn't have as much MAD - everything you need for one, you need for the other (maybe not Cha as much for Scouts).
Ninja/Rogue would wind up with massive MAD - Dex, Wis, Con, Str(probably), Int(for skills, not necessarily vital, but good to have). The only one you don't really need is Cha, but then you're not as good with several handy skills (Bluff to feint, etc. Disguise, UMD).
Scout/Rogue doesn't have as much MAD - everything you need for one, you need for the other (maybe not Cha as much for Scouts).