In regards to the first question, "curing" a UMMU is supposed to be handled by the vessel code. However, no-one seems to have developed any code to "cure" UMMU's. Some have developed code to injure a UMMU - but nobody has yet developed a "hospital" vessel.
When he created UMMU, Dan tried to make it as "open" as possible.He created ways for vessel devs to "injure" and "cure" UMMU's. He even provided examples of much of it. The DGIV can "injure" UMMU's. But the DGIV is a small vessel and doesn't have a "sick bay". The Arrow is big enough for a "sick bay" (that could "heal" UMMU's) but the Arrow is really just a "technology demonstrator". It was built to demonstrate many of the the abilities of UCGO and UMMU - but was not intended to represent a "finished" vessel.
What happens to a "person" when they are aboard a vessel is dependant on the vessel. A UMMU that is NOT aboard a vessel can be injured (by the UMMU code if certain limits are exceeded) but you don't expect a person to just "heal" on their own. They would need a "hospital" or "sick bay".
In short, Dan's UMMU enables both injury and healing - but nobody has yet implemented the "healing" portion of that. I suspect that this has to do with the fact that there is no "injured" flag - only basic stats (age, respiration, pulse). There is no clear way to mark a UMMU as injured.
So, let's say I create a Glider, like the DGIV or XR-series. I can use forces to determine if a UMMU should be "injured" - but a glider is too small to have a real "sick bay". To "heal" a UMMU I should have to transfer it to a hospital - or a ship that has hospital facilities (ie, a "sick bay")
So, when I create my vessel, I can keep track of the health of the UMMU's in the vessel - but when it comes time to transfer that UMMU I run into problems. I can't set a flag to show if the "person" is injured - or how severely injured they are. I could set the pulse or respiration low - but that only helps in a vehicle - vehicle transfer. If I "EVA" a UMMU the UMMU code will change the respiration and pulse depending - so a person may not "stay injured" while they are EVA'd to transfer from a vessel to a "hospital". Even if the transfer is vessel - vessel (ie, a DGIV docked to a "hospital" ship), I can't really send info on injury status. I can only send info on respiration and pulse - and there is no standard on what respiration or pulse mean to "health".
I'm not complaining about UMMU. It offers much that was missing - it humanizes Orbiter. You can transfer a crew - and crews can be injured (or healed) while aboard a vessel. It could, perhaps, be improved by adding a "health status" flag. It would establish a standard - and vessel/base devs would be able to create hospitals without having to create a standard (or worse - several different standards) on what pulse/respiration rates mean what level of injury.
I would like to see a simple health "flag" that offers a few simple options. Let's say flag=0 means good health. Flag=1 means minor injury - will improve slowly by itself or heal faster in a "hospital/sickbay". Flag=2 means a moderate injury that won't get worse but won't get better outside a hospital. Flag=3 means a severe injury that will get worse unless in a hospital (where it would get better).
UMMU, even as it exist today, has a lot of room for third party devs to expand it. Unfortunately, there is no real standard as to how those improvements should be handled. I think Dan was hoping that if he laid the groundwork, others would pick up the ball and run with it. Realistically, that isn't going to happen until someone sets the standard - and that won't happen. As the creator of UMMU and it's SDK, everyone looks to Dan to create that standard and until he does I don't see much forward progress being made.