Why that? Even if you do have 100 or 200 actual VMs, this is a 24 bit mask, that provides you with thousands of MAC-Addresses, you should be able to find a spot where you can safely start from, like 00:21:f6:01.XX.XX, that would provide you with 16k MAC-Addresses. You know, that the first three octets are reseved for the vendor IDs, so you can't freely grab from there anyway.
Found some references to the octets:
./servers/AdminServer/tmp/.appmergegen_1347446613061/ovm_core_188.8.131.525.ear/l014uq/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
./servers/AdminServer/tmp/_WL_user/ovm_core/t0yzcu/war/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
./servers/AdminServer/tmp/_WL_user/ovm_core/ttzie3/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
./servers/AdminServer/tmp/_WL_user/ovm_help/33se2m/war/helpsets/ovmHelp/vmusg-vm-hardpart.html:vif = ['mac=00:21:f6:00:00:00']
./servers/AdminServer/tmp/.appmergegen_1347446613061_ovm_core_184.108.40.2065.ear/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
./servers/AdminServer/tmp/.appmergegen_1347445734381/ovm_core_220.127.116.115.ear/l014uq/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
./servers/AdminServer/tmp/.appmergegen_1347445734381_ovm_core_18.104.22.1685.ear/doc/api/com/oracle/ovm/mgr/api/manager/VnicManager.html: Octets used are the OUI from the VnicManagerProperties(default value is 00:21:f6).
Hmm, changing vnicManagerProperties did not help. Am I on the right track?
Its not 16k it more like 16 million plus unique addresses.
If you're really concerned about the possibility of a MAC conflict, Segment your two managers/Servers on different subnets and create two different layer 2 environments. You really should learn the difference between layer 2 and layer 3 traffic. Once traffic is transported via layer 3 traffic.... the MAC address is only preserved. The MAC address is not used to "route" the traffic.
I understand this is probably quite late answer, but since I found you article by googling, and then found a solution to my problem (which is similar to yours) I decided to add information for the others.
The UI of the Oracle VM Manager restrict the MAC addresses that you can enter.
It turns out that if you import a VM machine (not a VM template) it allows you to keep the original MAC address. The same is true for P2V VM creation method.
If you have followed a support.oracle.com note about VM guest migration from OVM21 to OVM30 that you probably imported a VM template in OVM3, and then created a new VM, with one of the preconfigured VNICs. Actually you can create a new VNIC with whatever MAC address you want from the CLI (command line interface).
ssh admin@you-vm-manager-host -p 10000
create Vnic name=desired-mac-address network=one-of-your-defined-networks
Then you can edit you VM machine configuration and choose this address, instead of the one assigned to your VNIC.