Coffee, SS do not routinely visit because you mention ABA. I know this happened to Starlight, but it is not a general policy. We have been doing ABA for 4 years now with dd1, and have never seen a hint of SS, or any other hcp come to think of it.
ABA is a method of teaching, based on behavioural management. It breaks each task down into tiny steps, and is completely tailored to each child curriculum wise.
Dd1 will, in September, start at her second ABA school - it is possible to get LAs to pay for it, although a long hard fight and you need to be organised. We never tried to get our home programme funded, and did put dd1 into preferred LA provision to prove she would fail there (was a very difficult thing to do)
Vinnie: a good SN school may well use some ABA principles. It is not just using rewards as most parents would use them though. It is about totally changing the way you view reward and reinforcement, and using these systematically in a structured way - often the tasks set are far smaller than you could think possible (eg when we started toilet training dd1, her first target was to touch the door of the toilet - not go in, not open it, just go and touch it, get reinforced, and build up her confidence. Then we moved onto turning the handle, then opening the door but not going in, then going in and coming out again and so on). The bit that was overlooked by dd1s then Teacch based school was that, even though she was not exhibiting any anxiety when they took her into the toilet (she was never successfully trained at that school, BTW) she was so overwhelmed, and worried she did not know what to do that she could not take in new instructions. We started the whole task at a level we knew she could master (we use errorless learning with dd1, to combat self esteem issues) and it wad never a problem at home - the whole thing was enjoyable (!) right from the start.
It is north doing some proper reading o. ABA, rather than just anecdotes like mine or explanations from parents who use it - it is a good system, which centres fully on the Chris (but not in a EYFS child-led play way), and which uses reinforcement and motivation to promote the learning. It has done wonders for dd1