Just did an upgrade of CXO 4.0 to 5.0.3 and Agent continues to work well!
Have not tried a clean install, but did so back with Agent 3.x and a demo version of CXO 5.0 and that combination also worked well.
Notes: CXO 4.0 and 4.2 required upgrading the rasapi32.dll.so to run Agent 3.x. This tweak was not necessary for Agent 1.x or 2.x but presumably still is for Agent 4.x.
Yes, I'm an Agent beta tester... No, I won't talk:)