Do they work together? I'm not sure as Holomask is not really a marker/token state, as you are using a miniature.
I don't believe so. Surprise Attack says you need to be in Marker form (which Holomask is not considered to be) or Hidden Deployment to use it. The Holomask and Holomask State rules don't offer anything that contradicts this, so no Surprise Attack from Holomask state.
No troop that only has a Holomask also has Surprise Attack, whenever they obtain that Special Skill, it is because something else gives it to them (like Holoprojector)... it doesn't seem that Holomask allows to use it.
Note that you only get Surprise Attack when your Trooper Profile has it, and Surprise Attack requires that you are in a Marker state in order to benefit from it. Holomask is not a Marker state, QED you can't Surprise Attack just because you're in Holomask. Troopers with Holoprojector in the Holoecho State are in a Marker state, even if they are using actual models — note that during your active turn, when you'd be able to declare Surprise Attack, you put down a Holo marker to indicate your trooper is in Holoecho State, which is your cue that it's a marker state even when using models for the holoechoes.
