It suppose that you should not do that... and the tac will not help you if something bad happen...
But you should be able to upload the firmware upgrade but with the aruba firmware on dell AP
I have seem Alcatel IAPS with ArubaNetworks firmware....
I did not do that myself.. the client did themselve...
So like i told you if they could do it you can do it i guess... But have in mind that TAC will not help you if they find out this.
Cheers
Carlos