That is possible, but I think the high costs for constructing a large amount of Icenis wouldn't be worth it. The amount of technology and resources that goes into creating a small ship with the amount weaponry, armor and engine power that the Iceni possesses probably means that creating one might be just as strenuous as creating a destroyer or several corvettes.
I think it would be more feasible for the GTVA to just create more Hecates and Orions - Fighters and bombers are the main combatants in FreeSpace, so creating a ship capable of ferrying them around would be more efficient than creating one small pocket destroyer that can't really do that much save for run around and escape.
You also have to take into account that the Iceni isn't really much good in a defensive sort of position. Sure it has a lot of firepower, but before long you'd soon see that having more fighters and bombers would be more effective in creating a better defense of a Jump Node or installation. The Iceni is more fitted to running away and offensive missions - Perhaps SOC mission strikes deep into enemy territory, much like the GTFf Saphah of Derelict.
Really, I can't see a widespread creation of Iceni like vessels for the GTVA, at least not in the numbers you're suggesting. If they were created, IMO they'd be used as a rare forward-attack craft for strategic assault missions in conjunction with a few heavy fighters like the Ares or Erinyes. I don't think Icenis would be used in a large, numerous support role due to large construction costs as well as its inability to really do that much good in defensive missions.