It's not the gameplay mechanics that raise a flag for me.
It's the art. Compare the screenshots of the various units to this:
http://warhammer40k.wikia.com/wiki/File:Ultramarine_terminat...
It's the art. Compare the screenshots of the various units to this:
http://warhammer40k.wikia.com/wiki/File:Ultramarine_terminat...
However, it's telling that GW's notoriously trigger happy lawyers have left Blizzard alone, so it's pretty much a non-comparison.
While the visual similarities haven't causes Games Workshop to complain about infringement from Blizzard (as far as I know) it doesn't mean that Games Workshop isn't complaining about infringement in this or other cases.