It's actually not well specified in the rules as written. Most tournaments FAQ that snikrot and ICs cannot be combined.Vas you are incorrect according to tournament rules. This is due to Snikrot's RaW: Ambush gives the ability to his unit thus the boss gets it as well if he is part of the unit. RaI may be the other way, but you must play RaW when you can.
I have run Ghazskull and Snikrot... It is cruel and funny to play.
If I could be bothered I would link you to all the tournament rules. I have also asked the red shirts close to me and they all agree (about 20 or so guys), it is a pain in the ass rule, but it is a very real and scary way to make a list
Also if you go searching on these interwebs you will see most forums have had this arguement (Warseer, LO, dakkadakka) and they have all come up 1 way. Snikrot can roll with a HQ from behind.
I found the latest one because I knew they changed their mindsFun thing I found, in the Adepticon INATFAQ (the FAQ used by Adepticon, pretty much the biggest warhammer tournament, and generally pretty widely accepted in the tournament scene, specifies that ICs joining a painboy's unit do get FNP. (In the Ork section)
Oh, it also specifies that no one can join Snikrot's unit and benefit from Ambush.
Like I said, it's not well defined. Without an official GW FAQ we'll see rulings one way and the other.I found the latest one because I knew they changed their minds