I did this after a fashion in one of my mods, where the Pathfinder started off as normal, but with some upgrades it made him prone down and leopard crawl on the ground (using hiterto unused model animations) and also gave him a slower locomotor which had a speed below the MoveThreshold speed of the StealthUpdate module, so he remained stealthed when moving.
If you want to see the mod, it is SoupedUpGeneralsMod_v104
Cncmaps : Generals Zero Hour maps : Command and Conquer 3 maps