Hi Pete,
I did try hooking a grid tie inverter to my powerjack, just to see how it would do. Didn't go so far as building safety circuits to regulate it. Just watched it closely. Didn't have enough solar hooked to the grid tie to worry too much about.
Anyway, it worked ok, but seemed to me to make the system more complicated and possibly unstable than it needed to be. I can power the house with the powerjack just fine, and it's (usually) trouble-free.
As for those safety cutouts, my understanding from those who tried it, was to not disconnect the gti from the powerjack, because when it re-connects you get the 5 minute startup delay of the gti. Instead you interrupt the solar to the gti, which leaves it connected but not producing. Same result but smoother operation with no 5 minute deadtime each time it throttles back. Same as if clouds blocked your panels.
I think lighthunter did some work on those things, with good results.