In The Netherlands I have also started to translate LOINC database items to Dutch. I ran into the same questions that you address. I choose to translate 1H to 1u (uur). In a way we follow UCUM, but also in Dutch we never use “U” for “uur”. That is not a problem, as the language variant is only used in your language area. When you exchange the LOINC code with an US lab, they will read the US meaning in their database.
I asked Daniel Vreeman about translating umol to µmol (all uses of u instead of µ). Daniel advised to keep using “u”instead of “µ”. This item is sent into the message so it depends on the computer codepage of the receiever if the code for “µ” is also a “µ” in their code codepage. If everone uses Unicode then it may be solved (I guess). For the time being we use “u”.
NVKC, The Netherlands