omission of に when its used with もらう

Question

デンジ君は早川君の部隊に入ってもらう

デンジ君には早川君の部隊に入ってもらう

Any difference?

Answer 1

There is no difference in meaning.

Grammatically the subject/topic of the first sentence is デンジ君 and the subject of the second is the implicit I. Thus they roughly correspond to

1. Denji shall be in Hayakawa's unit.
2. I will let Denji join Hayakawa's unit.

In both sentences, もらう indicates the speaker benefits from Denji's joining the unit.