May a Non-Jew be honoured to open the Aron Kodesh? If so, is he permitted to wear a Tallit at that moment?
I think that it is inappropriate to have him open the Aron Kodesh—unless there is an extenuating circumstance- but I would want to research more parallel situations- for example, there was a long standing custom to present kings with a Sefer Torah. He may wear a Talit. There are probably no direct sources for any of these answers- however, in general a gentile may fulfill Mitzvot if he chooses to- except for learning Torah and observing Shabbat.