I've been browsing through Street Magic, and I've got a question about insect spirit powers.

It's fairly obvious True Form insect spirits get them. It's also fairly obvious Flesh Form/Good Merge insect spirits get them.

Do Hybrid Form merges? Or do they only get the skills and the Force boost to physical attributes?

Yep, the only mechanical difference between the types is the Inhabitation-related powers they get; True gets Astral Form, Hybrid just gets Immunity to Normal Weapons, and Flesh gets Aura Masking, ItNW and Realistic Form. And their stats are different if they're True Form, obviously.