IPAM can get MAC information either by using SNMP against an individual IP or by using Neighbor Discovery. Neighbor Discovery is a new feature in 1.7 and allows you to specificy a router or "neighbor" device which has information about an IP address. You add a neighbor device on the properties of a subnet.
For more information on this new feature, you can find the documentation here.
mav as a side note the neighbor scanning link just links to perhaps the most comical help page ever.
Ozzy, not sure if you've found what you were looking for yet but IPAM with this feature turned on will indeed pull macs but they are not displayed by default. you would need to edit each ip to see the details. you can add the column to the default ip view by clicking top left