UAC is not an anti-virus but I can see what you mean. You should have some form of anti-virus in operation regardless of whether you have enabled UAC. Disabling UAC will not interfere with the proper operation of installed anti-virus software.
However, disabling UAC will increase your vulnerability to security holes in applications running as administrator as well as "trojan horse" type programs. Be careful with what you download and keep your applications current with security updates and you should be fine.
It's the old security vs. convenience tradeoff. You can never have both, even if Apple would have their users believe otherwise. The wakeup from that one will be harsh I fear
