So, the leshy familiar enters a room wherein resides a vampiric mist. When the VM senses blood, it goes after whatever creature has the blood. Would the mist react at all to a leshy?
That sounds like it is entirely up to GM discretion.
There was a whole debate thread on what creatures and ancestries are immune to bleed damage because they don't have blood. Leshy was one of them that was argued as not having blood.