Yeah they're basically bucket shops tbh..
Almost certainly they're not going to hedge most client trades - average trade size would likely be smaller than they can directly hedge anyway, probably more just concerned about their overall inventory risk. Various firms seem to have implemented some form of dealer surveillance tool - one of my mates was involved in developing one at a large SB firm years ago - just the process of flagging up a customer's orders to a dealer inherently slows them down significantly and of course a human dealer is prone to slipping prices when it suits and/or giving adverse fills instead if it goes against the customer etc..
One thing they used to be concerned about is scalpers - not random day trading idiots but people who might use their own price feed and spot where the SB/CFD firm is slow to update prices the try to pick them off - though easy enough to catch those people and things like dealer surveillance tools will instantly ruin their game. Not sure that is so feasible these days but years ago they'd not be on top of everything when trying to stream prices for hundreds of different products and just like a regular bookie someone paying attention could start picking off some of their quotes etc..