Ryan Anderson would help the team with his shooting on offense, but his defense is too paltry to play him more than 24-25 minutes a night, so the problem of not having a consistent starting caliber player would persist. Not really sure it's worth it.
If the Celts trade a big man, they should be looking to add wing depth, or trade multiple players for an upgrade in the starting lineup. Probably not worthwhile otherwise.
Plus like it or not, Sullinger is the only big we currently have that gives us a semblance of quality minutes at center.
So with this trade our biggest problem, defense from our bigs at the center position, would be even worse all for a half a season Anderson (expiring contract), so we miss out in whatever benefits a Sullinger restricted free-agent would give, and Anderson would also have a bigger cap hold than Sullinger for free-agency so limiting our options a bit more.
In all, don't really see the benefits. If we want more shooting, just play Olynyk more.