Accordingly to the documentation - The Dude v6/Agents
Starting from RouterOS 6.38.x any RouterOS device can be a Dude agent without any installation or configuration required
And Agents should be directly accessible and in case of front router it will require a Winbox port forwarding.
You can forward Winbox port on front placed router/firewall to your RB750r2 and then add it to Dude Server for monitoring and also use as an Agent.
Dude Server --> Router --> RB750r2
But probably it is a good idea to do some tests before implementation, because on the forum we already discussed related issues Dude server v.6 - not working with port forwarding
and Dude - Device RouterOS on no-standard Port