The same is true of P2SH addresses. There are a much smaller number of script hashes than there are of possible scripts. Any script which hashes to the same value as your multi-sig set up will be able to unlock the coins contained on that address. So technically speaking multi-sig addresses are just as vulnerable as non-multi-sig addresses to an address collision, but since an address collision will not happen before the extinction of the human race, I wouldn't worry too much about it.