Yo Noodlearm,
I have a Scag Wildcat. It is rated for towing and has a place for a hitch ball, but I've never used it for towing. So, I guess it might be able to pull your swisher deck ....but I'd guess a tractor would pull it better.
The biggest advantage of a ZTR (IMHO) is the manuverability. If you were towing an extra mower deck, I'd guess the manuverability would go out the window. You'd have to make wider turns just like you do with your GT.
With a ZTR since you can turn on a dime, you can zip back and forth and keep the blades on grass that needs cut 90% of the time. This makes a huge difference. In my case, the 61" ZTR mows faster than my kubota with a 72" RFM. An hour faster for mowing 4 acres. I was sure surprised. A big part of this used to be a tomato field, and is slow going for the ZTR.
Another plus is that when you decide to add landscaping to that open field, a ZTR makes it so much easier to trim around stuff.
Hope this helps,
Moon of Ohio