Can I set IP rDNS / PTR records?

Yes, reverse DNS (or PTR) records can be set from VPS Control Panel --> rDNS, all changes are instantly updated.

The record must be a FQDN (Fully Qualified Domain Name) and it should have an A record pointing to the IP.

Note: If you would like to set a rDNS record for your cPanel hosting account which includes a dedicated IP, you must submit a ticket.