If blanks are allowed it should be very heavily managed to be safe, and rules should be very clear about taking hits and so on.
Milsim West allows blanks (with heavy checking and there is designated blanks marshal), but it has a 20 foot dome shaped no-engagement-distance (from the muzzle), and hit taking is totally optional.
I think my point is, people should be able to know beforehand blanks are involved in a game and how it is managed so they can decide whether to take part, rather than trying to find out the rules mid game. If the rules are unclear or non-existent or unenforced, this is totally a field management issue. If the field has management issues I think totally up to customers to point it out and openly talk about it. If every field has management issues, perhaps we need to talk about it even more.