If port-channel is working as it's supposed to, the physical links in the port-channel will operate as a single link. So, whether a port-channel creates a L2 loop depends on your overall topology, and again, that everything is working correctly.
Even if a specific port-channel is working correctly, something like Loop Guard can protect your from other link issues, i.e. including non-port-channel links. Ditto for Root Guard. I.e. both Loop Guard and Root Guard are intended to preclude issues beyond those of a problematic port-channel.