It depends.
The canonical form of a DPID is without a hyphen. Hence DPIDs should be used, in DDEX messages, without hyphens:
Do communicate DPIDs withOUT hyphens
<PartyId>PADPIDA3897722461G</PartyID>
Do NOT communicate DPIDs with hyphens
<PartyId>PA-DPIDA-3897722461-G</PartyID>
However, for human consumption hyphens may be added. Therefore, the HTML/PDF export of the DPID registry contains hyphens whereas the XML export does not.