Hi Carl.
I was searching for something and came across this, since it wasn't answered I figured I give it a go. This comes with the caveat that there are tons of people way more qualified to answer this than me. I also realize it's been months since this was asked and it's probably not needed anymore, but just in case plus for others searching.
I would say it's technically safe to do so, but probably not recommended. I've always seen (by either myself or more importantly others) a separate switch. One misconfiguration or someone plugging into the wrong port and you could have a problem. If you have a separate DMZ switch that's clearly marked it's much harder for someone to accidentally do something to it. They'd have to go purposely go log into that switch and make a change instead of say accidentally including the DMZ ports in a VLAN change of a range of them or something. One guy at a pretty big company got some of that black and yellow hazard tape and put it around his DMZ switches. I always got a kick out of that. Come to think of it, I think I need to find some of that tape.
Ted
