How does the Infinispan OSGi integration look like?

Brett is building it, there was something in place but very limited and essentially not functional.

I see Search more as an add-on which needs to play nice with whatever ORM or Infinispan provide.

Exactly

How does Infinispan Query bootstrap Search?

Can't tell you that. It's top secret source code :-P
More seriously: all the details are on github but I'm happy to give you an overview via voice; would be good though for you to setup that project to have an occasional look, would be useful to clarify many other things too.

How does Infinispan Query bootstrap Search?

I was referring to the tests that Brett made for Hibernate ORM: a great resource for us to understand consumption of an Hibernate service, but I don't think we still have something like that for Infinispan? Actually maybe that's what Brett is working on now since he's having an experimental branch of Infinispan to port it to OSGi.