Until one is proficient in using the autopilot it actually increases the workload.
Best to get some practice in with an instructor before using it for real in IMC.
As for not using a simple autopilot in order to retain flying skills. I would not worry. For a simple 1 axis autopilot, the pilot still has to manage the other 2 axis as well as the navigation of the aircraft. Any proficient pilot will be able to trim out an aircraft with no autopilot and fly hands off for long periods in IMC be it climbing, descending or straight and level.
It's not about flexing muscles to control the aircraft. IMC flying is all about management of the siutation and keeping one's mind well ahead of the aircraft.
If you are dealing with a full 3 axix autopilot with altitude capture, vertical speed modes and coupled navigation and approach facilities then I would agree that long periods without some hand flying would reduce motor skills. However, the mental skills which account for a big percentage of IMC operations would be stil up to speed provided that the autopilot was not being used as a crutch to support a person who lacks the basic skills to start with.
Pilots who use RANT on a regular basis will have better situational awareness regarding procedural flying than many others who do lots of aircraft flying. The reason is that RANT allows more brain time to think about what is going on. With practice many issues become almost automatic and that releases more thinking time for other things like flying the aircraft. An example of a device that is not even in the aircraft that regular use helps not hinders IMC flying.
To sumaraise; Get training from an instructor and with thorough knowledge of the system and it's legal as well as operational limitations make the most of it.
Regards,
DFC