AFAIK Blackwater was mostly for guard duty, but I'm sure in practice it wasn't just for that. There's also a lot of smaller orgs out there that do "guard duty", not just american (for example britain is also active).

Also there was a point when Blackwater boasted that they could deploy a light brigade (~3k troops) anywhere in the world, people in the Pentagon figured it out and very quickly killed that org. Compare with Prigozhin and his adventures, just for reference he had more than 10k soldiers under his command, on heavy equipment (arty, tanks, ifvs), permission to illegally recruit from prisons, he even had air defence like Pantsirs, the motherfuckers even tried to get nuclear backpacks (man-portable nuclear bombs) from a storage site near Voronezh.

I think those entities are being tolerated and even welcome, as long as they don't exceed some potentially threatening size.