the ARM server is also a DHCP server

It is. However, it waits until the Receiver has asked for an IP address 5 times before handing one out. This means that it is exceedingly unlikely to hand out an address before your "real" DHCP server does.

Thus, if your "real" DHCP server isn't handing out an address -- that's a problem with your server, not ARM.

OTOH, you can turn off the DHCP server in ARM by following justDave's instructions.