[grace-baker Hexnode 26 November 2019 grace-baker Moderator]

Hey, Thanks for posting the question.

I’m afraid it is not possible to create an Apple Business Account without the DUNS number.

You can still manage iOS devices using Hexnode. If you want the devices to be supervised without using ABM, you will have to enroll them using Apple Configurator 2.  Over-the-air supervision is however, possible only for DEP enrolled devices.
The other enrollment methods are:
1.Enrollment without authentication
2.Email/SMS enrollment
3.Self-enrollment or Active Directory-based enrollment

Please use the help link to know about the enrollment methods in detail.

Cheers!
Grace Baker
Hexnode MDM