The NPS configuration looks correct. When it's in DVLAN mode and a client is connected to the AP, look in the Monitor>Currently Active Clients page and see if the ZD has identified the client to be on the correct VLAN, from the above configuration it should show up as ACCESS VLAN 501, but verify.
If the client is identified as being on the correct VLAN, it means NPS setting works, the ZD received the VLAN setting correctly, so the next step is to figure out why the client is not able to get in IP on that VLAN.
Check the switch port the AP is connected to:
1. Is it set to trunk mode? Management traffic is untagged
2. Is VLAN 501 configured as an allowed tagged VLAN on that port
3. Is there a DHCP server on VLAN 501 already
If you configure a switch port for Access mode VLAN501 adn plug a wired PC to that port does the PC get an IP in the VLAN501 range?
Post the switchport config as well.