SP uses EPDM o-rings and christolube in everything anyway, so as long as it is properly cleaned you should be good to go.
The qualification here is the same one that applies to any diaphragm reg used for O2 service. You have that enormous diaphragm that will potentially be a fuel source if an o2 fire occurs. What is worse is that if a fire occurs, the diapgram ends up being a route for flames to exit the reg on a large scale basis.
In contrast with a flow by piston reg like the Mk 2 or Calypso, all you have are a couple o-rings exposed to 100% O2 and if they get charred you still have very little fuel and fairly tight clearances so what you get is a flash fire inside the reg and then a leaking reg - not one spurting flames.
People always seem to be trying to use diaphragm regs in applications where they do not make sense and a deco reg for 100% O2 use is a prime example. Realistically, the Mk 2 works great on ice dives, so as long as you are not using medical O2 (it potentially has more moisture than aviator or welding O2) you will not have freezing issues (and if you use medical grade O2 with higher moisture content, your diaphragm is not protecting the inside of your reg anyway).
Plus, cold water usually has thermoclines so your 20 ft stop is usually going to be 40 degrees or higher where freezing is less of a concern. Also, your workload is by definition lower than on the bottom so the lower flow rate provides a much higher margin to prevent the reg from freezing up.
------
Your Scubapro versus Aqualung/Apeks self service argument is actually not valid. Aqualung/Apeks also controls their parts and in fact does so far better than Scubapro. Go on e-bay any given day and you will find at least a dozen Scubapro kits for sale compared to usually zero for Aqualung or Apeks. They rarely show up for sale and Aqualung/Apeks will not even sell kits to former dealers trying to honor customer warranties. So if you think owning Apeks will make servicing your regs easier over the long term, you are mistaken.
If you are into DIY servicing, Scubapro is THE brand to have as:
1. parts are readily available from a variety of sources,
2. specialty tools for them are available from 3rd party sources,
3. SP has a track record of supporting discontinued regs for decades, and
4. SP uses just a few kits for all their regs with most sharing common parts and o-rings making logistics a lot easier.
