Not really. Port Adelaide are a very old club that negotiated to join the AFL behind the backs of the rest of the SANFL in the early 90s. When the other SA clubs found out it created a big ruckus and the AFL agreed to let the SANFL form it's own team to enter instead. Thus the Crows were born, and Port Adelaide ended up being admitted in the late 90s. The only comparable situation in football is the NSL clubs that were upset over being overlooked for the A-League, but Adelaide doesn't have that as United was actually set up in the last season of the NSL after Adelaide City dropped out. City have spoken about wanting to make a bid for the A-League, but they would be relying on current fans and anyone else they can engage.
Edit: I should also add that Aussie Rules is the big football code in Adelaide, the SANFL final usually gets over 30,000 in attendance.