I guess yes, due to the way it's worded. Any creature. And they don't have to view their reflection. Literally just look at the mirror itself. No limit on how many creatures, and it only takes 1 charge from the mirror per activation, not per creature healed:
When the command word is spoken, any creature viewing the mirror receives the benefit of a heal spell. This requires the use of 1 charge; the mirror has 10 charges when created.