Hi,
mark Freeradius@OPNsense -> general -> Enable Mikrotik attributes and set Mikrotik VLAN attribute. This works also for Aruba access points from 5xx series. Be aware of "VLAN ID" and "Mikrotik VLAN ID" should match, otherwise you may get IP address from DHCP server behind "VLAN ID" or other strange things may happen.
regards
ip6li