Does anyone know if there is a way around this and enable proxying on example.tld with the mail server at the same location?
AFAIK, this is not possible since Cloudflare does not support proxying mail.
We are using Vultr for the VPS, so rDNS needs to be setup to reflect the server host (EX: example.tld), if pushing the mail server to mail.example.tld, the rDNS would need to be updated to that.
Correct. You have to set the rDNS to the name of the mail server in Vultr.