The central focus of the discussion will ultimately come down to a PM/owners perspective, or the testers/users perspective.
As a certified tester I would almost always require a separate environment, usually including separate hardware.
If for any reason this cannot be reasonably achieved (cost/schedule/availability etc) then I would require a very robust configuration management plan that would specify access, availability change control process etc.
Ultimately, without 1 of those 2 things, you will end up with rework, unnecessary extra maintenance etc, due to shared environments.
If the software/system is being prepped for production, I would certainly expect some level of 'control' from a testing perspective, but that could vary based on what the system/software is.
A radio controlled car is not nearly as significant as say a flight control system.
If you are a tester, and your gut is telling you something is wrong, follow your gut!