is there anyway to configure DMVPN with digital certificates and make the Hub router to act as a Certificate Authority server?
Yes, you can do that, go ahead and configure your Hub router with the normal DMVPN setup so that it becomes the HUB. After you have done that follow the link below to add PKI server features:
And to enroll the spokes to the hub use this link:
Remember that regardless of the Hub router being the CA authority, you need to enroll it to himself to allow IKE PKI authentication.