That depends how good the boxing coach is. Most of the time a pure boxing gym will get you hands that a muay thai gym couldnt even come close to giving.
Well depends on the Muay Thai coach too... most modern MT teachers have absorbed western boxing in its entirety, so you have the full jab/cross/hook/uppercut/overhand and defense arsenal from Boxing built in to MT, but with a modified stance etc. to account for kicks and knees.
If you're talking traditional MT that has weak hands and emphasizes knees and elbows over all else, then yes, but modern MT already has boxing built in IMO.
The rest of the stuff a pure boxing coach will give you is for sport purposes anyway and not much use in a street fight. For example full bobbing and weaving, peek-a-boo type defense, clinching without offense etc. is suicide without gloves or rules.