I would say yes weigh it in, I would also argue if someone else had hooked his rod and landed the fish they should count it too.
Had two very strange things happen on Bolingey last week, first I hooked into someone elses rig whos elastic had broken and landed a fish about 11lb which was foulhooked, so I sort of foulhooked a foulhooked fish. Later, after landing a carp of double figures I took the hook out and dropped it in the margins, it was bare as I was using paste at the time, whilst I returned the carp to the lake from my landing net, as I picked up my top kit the elastic tore out and a very angry lip hooked lump soon graced my net,
I just sat there bemused for a few minutes wondering how the heck it all happened!!