Thought I would report this issue:
Trying to set up DHCP-only access on a dhcp server which is listening on a VLAN interface. I set add-arp on the DHCP server and set arp=reply-only on the vlan interface.
As soon as I did this, the router stopped responding completely, on all other vlans/interfaces, and was not even able to telnet in from winbox on management port. The router returned to working after a power-cycle, and it did not preserve my setting of arp=reply-only on the interface.