I too am an IT pro and as it stands two weeks ago the supplied Cisco Comcast cable modem does not support bridge mode. It NATs and then you can plug their router in behind it as well as your own, but either way you end up double-NAT'd. I was told a firmware fix has been developed and should be out "soon," but the technician also indicated it had been delayed several times.
Yes, as it is it's a problem. I haven't tried to move the security router behind mine, but there are zero obvious settings in the cable modem (DMZ, forwards etc) that would imply it would be an issue. I am not using cameras with the system though, so that might be the limitation.