When creating a DHCP Fixed Address, you have these options: MAC Address DHCP Client Identifier It does look like you can fix an IP to a client by the Client Identifier. You would have to test it out to see if it works.
Thank you TT for taking the time to answer. I created a ticket by Infoblox, who told me exactly that. Btw the Dhcp config is viewed in "Dhcp/Members/ (right bar). Hope this will come in handy for future similar questions. /JanV