I can only speak for HW:B1, firmware 2.02NA, Dir-825.
No.
Disabling "DNS Relay" allows the DNS entries from your cable-modem to "pass-through" to your clients. With "DNS Relay" disabled, you should see a couple of IP addresses external to your network on your clients. With "DNS Relay" enabled, the client DNS says "192.168.0.1".
Note: If you disable "DNS Relay", but still have clients with DNS of "192.168.0.1", on Setup/Network (on router), go to bottom of the page and revoke the applicable client IPs. When they re-connect, they should have "real" DNS addresses.