I don't know if Lasme would be competent as a back-up 3. And if he isn't, then he's not needed.
I'd like to see more of him matched up with a reasonably quick swing man out on the perimeter while on defense. When he was matched up with Andre Iguodala, that was informative, but it didn't last long enough. Unfortunately, Lasme has been mostly matched up with 4's down by the block.
All the same, even if he can move his feet well enough, Lasme wouldn't be a rotation player if Pierce and Daniels are whole and healthy. But if one of them isn't, then sure, he could play fifteen minutes a game as a back-up. I don't see him as having an incorrectable foul problem. In the last game he picked up two moving picks. That sort of thing is correctable. And I think he's better than medicore as a rebounder. (Wafer would be sub-mediocre.)
As for a specialy spot defender, I've never thought he was better than Pierce, or necessarily, even than Daniels. But fouls, tweaked ankles, and numb shoulders do happen. And when they happen, I might prefer to turn to Lasme than to Wafer. But again, I haven't seen enough yet. And it's bugging me, but I expect tonight he'll be given his chance to sink or swim, and I won't be able to watch it.