I don’t know what Rush’s sources are, but he is 99.8% (or somesuch) correct, you know.
Here is what I found with a very quick Google lookup: http://www.thegatewaypundit.com/2016/03/rent-a-mob-supplier-to-move-on-org-and-other-soros-related-disturbances/
There are other links to LIEberal “Rent-A-Mobs” on the internet.
It is a known tactic of the LIEberals — I,myself, and my fellow WDC Chapter FReepers faced them down many times in the 1990s and early 2000s.
I can tell you that they are ugly, nasty, dirty, rude, crude and thoroughly obnoxious! And, they smell bad!
My experience of them has been the same as yours, and I know about leftist rent-a-mobs generally, but I think without specific evidence Rush is wrong on this mob. The money for their hiring is aligned to what this mob is outraged about.