I'd say a summon could be used as a drive form since that's similar to how Sora got his drive forms, outside magic. Summons could give you outfit changes that increase your power and lets you tap into theirs, but depending on how powerful the summon is there may be drawbacks to using it, similar to Sora's AntiForm, as well as a cool down/weakened state time.

And I'm sorry everyone for the delay in the GM post. Things got unexpectedly busy, but I'm free today and tomorrow for the holiday so I'll also respond to Hoshi in the collab.