Hi,
You should have a look under "Mixed Authentication Modes" in Aruba OS UG 6.1, page 323.
There is a command in the AAA-profile called l2-auth-fail-through;
"Use l2-auth-fail-through command to perform mixed authentication which includes both MAC and 802.1x authentication. When MAC authentication fails, enable the l2-auth-fail-through command to perform 802.1x authentication."