There shouldn't be any issue... the requirements for when you have an AP failover, is the the AP Groups are defined on all WLC's, the WLAN's are created the same, and that you have mobility up between the WLC's.
Could possibly be v7.3, which is deferred like v7.5. I have 2602's on WLC's running v7.4.121.0 in local and flex with no issues when testing failover.
Thanks,
Scott
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