Cool stuff!
Ok, I gotta ask - what is the 'mantis hand'?
Is it different in the various forms of SPM/NPM?

hmm...what comes to my mind is the shape of our hands. Fingers slightly split apart and arms/hands that seem to welcome the opponent into a trap.

Maybe something like this image?
http://www.markusmcb.co.uk/chowGar/images/grandmaster_yipsun.jpg

I dig how that "mantis hand" looks. I always thought mantis (n. and s.) looked pretty dope. I've seen this s. mantis practitioner doing push ups on phoenix eyes. Pretty sick.

Phoenix Eye fist: http://www.martialartsgathering.com/foto/chu-ka2.jpg
Except that the SPM guy's thumb was supporting the extended knuckle.

http://farm1.static.flickr.com/98/211731600_1b65629689_m.jpg
I just thought this guy was a badass.

Yeah, I think that's it. Here's an example of a guy using it in a chi sao match -
http://www.youtube.com/watch?v=FqoFQgJl1Yc
He's a fut sao guy under James Cama, so there's more than likely some SPM in there (Cama trains/teaches SPM as well as FSWC)
Is there any application advantage to the hand technique in regards to contact, energy, position etc?

Yea, that's Peter Bonet. He's pretty good. Cama, from my understanding, doesn't really teach fswc any more. He's real heavy with his s. mantis. Bonet got disqualified from that tournament for kicking a dude in the throat. I don't really like his style too much. Too flashy. Nick's chi sao and forms i think are my favourite. Same competition as the one you linked up there.

When caught between the ribs, the receiver will notice immediate contact. It's really good for shots to the face where knockout points are. Pressure points along the arms are great to attack with this fist in a chi sao. I always add them to my punching rounds. But unlike in that picture I have my thumbs supporting my extended knuckle. Focuses the energy, in my opinion, better.

Yeah, I watched a lot of vids from that competition and I gotta say, the mantis guys are using the WC footwork better than the WC guys, which is pretty telling of WC training these days. I saw way too much stiffness, forcing, leaning forward from the waist - but no real Biu Ma pressure going on, thus making a lot of attempts to take the center useless. That guy nick seemed to have a much better grasp of triangulating his attacks, getting control and working his way in. Liked his footwork a lot.