It works, thanks Keven. This is what we did. We took a HP Aruba IAP-205. Connected it to a seperate switch and router (for dhcp). All the Dell Aruba's W-AP205 have firmware DellInstant_Taurus_6.5.4.3_61959 and we pushed this same Dell-firmware also in de HP Aruba's. After restarting the HP Aruba it shows up as a Dell now. After connecting the new Dell (HP Aruba) to the network it get's all the settings from the master. Also roaming is working fine. I can't find a problem.
One thing. When flashing the Dell firmware in de Aruba make sure the Aruba is the only access point connected to the switch. That's why we used a seperate switch (network). Because when you put two Aruba's to the switch the firmware updating is going fine, but for some reason you can't logon to the flashed Aruba. The name or password is allways wrong. That's no problem, just disconnect one Aruba and restart the other and you can log on and it is working fine. Just do one at the time.