Reminds me a bit of L4D, but I loved L4D's multiplayer so no harm done. Also a seprate team worked on the multiplayer so the SP wouldn't be affected at all. So this won't hurt anything, it may even add longeitivity.
I hope that Dead Space 2 multiplayer allows local/splitscreen. Always a pain when it's online only; one more game I can only play with strangers rather than friends.