I'm sure i checked this with support after my initial post and it wasnt an RFE.
I will try this iRule in our environment also, as we are still with GSS and will be for the next year until we get GTM in.
What i did in the meantime was change the GSS poll to a HTTP HEAD type. This just acts like a user then and sends a HTTP GET to the F5 and consequently the servers, if there are no servers then the F5 fails the poll. The only issue i had here was with HTTPS polls, so i had to set up a second vanilla VIP called _gss_poll_virtual_server (a HTTP VS) with no dependencies, and an iRule to either accept or reject HTTP requests depending on the active members in the HTTPS pool.
This is a bit of a pain frankly if you have alot of HTTPS Virtuals, but its easy for the HTTP ones.
I will try the iRule mentioned above and report back, it needs to stop the 3-way handshake completing for a TCP GSS poll or it will not work (as mentioned by Steve@yellowbook). I am also confused by the CLIENT_ACCEPTED as i thought that was post handshake completion.