I'd say the most 'traditional' bar at Rovers is the Robins Nest (it's been open much longer than the East Stand bar anyway). This is situated under the Roger Millward Stand (or whatever it's called these days!), to the left of the player entrance if you're stood in the car park facing the stand.
I've not been in for maybe three or four years, but last time I did it had gone from been RSG members or pass holders only (can't remember which) to open access, but obviously you're best checking more officially if possible e.g. ring the club.
I'd say you'll be made much more welcome in Hull colours in the Robins Nest than the East Stand bar without a doubt. There is also the Harry Poole bar upstairs in the West Stand and Flannagan's Bar I think, but I know very little about these unfortunately.
So basically, I'd opt for the Robins' Nest if I was yourself, but phone the club first and check it's still open-access.
