Difficulty forwarding to F5-DNS in Azure

I'm by no means a GTM expert, but I'm assuming you created the following resources:

Local DNS Delegation subzone (ex. wip.domain.com) with the GTM Self IP as the Delegated Name Server

Local DNS CNAME (ex. site.domain.com with canonical name site.wip.domain.com)

GTM Wide IP (ex. site.wip.domain.com)

In this example, site.wip.domain.com should resolve properly and bypass Local DNS. If this doesn't work, something is missing on the GTM (or maybe a Firewall rule blocking DNS traffic)

If site.wip.domain.com resolves properly, but site.domain.com doesn't, something is missing on the Local DNS server (or maybe a Firewall rule blocking DNS traffic)