Can a DHCP reservation use an IP address in the exclusion range?

It will get the address. In one network I manage all of the reservations are in the excluded range.

From the technet docs.

http://technet.microsoft.com/en-us/library/cc737055(v=WS.10).aspx

Reservations can be created using any IP address in the scope’s address range, even if the IP address is also within an exclusion range.