PhysX support wouldn't change how things look on people's screens in terms of where enemies are. The carriers would still have to sink at a predetermined damage level due to the online environment. The support would only add visual goodies to the client side of the game. If you didn't have the card, those goodies would not show up, or would be less detailed. If you watch videos showing how PhysX works, it basically processes where an explosion would throw debris, how clouds react to their environment, etc. etc..
In my opinion, the amount of work it would take HiTech to add PhysX to this game would make it not worth it. It's hard to design a game where a hardware component is optional. There is always going to be some disadvantage or advantage to having or not having that piece of hardware. I don't know of any games to date that have been updated to support PhysX, which leads me to believe it either isn't possible, or isn't cost/time effective.
My $0.02