Is there a ruling on whether hybrid form insect spirits can walk on walls and ceilings? SM is pretty clear that true forms can, but what about hybrids?

That sounds like something firmly in the realm of GM discretion, to me.

Materializing spirits can ignore gravity and move in whatever direction they want whether there is a surface to support them or not. Hybrid spirits can't do that, and have to walk, jump and climb like the creature they inhabited.

Now they are crazy strong and have extra bug parts, so if you want to have them cling to walls and ceilings like Aliens I would say that is awesome. Not fully supported by the rules, but not outside the realm of possibility so I have no problem with it.
Having the foot and hand pads of hybrid fly count as gecko tape for example, is well within the kinds of crazy I expect when I go into a next to kick ass and chew bubblegum.

-Frank

What Frank said.

What Frank said. Plus I'm all out of gum.