Is the Walker LP system necessary if one already uses a good RCM?

Absolutely not. I have become to believe that the most important aspects of record cleaning are vacuum drying and avoidance of used fluids. How you agitate the fluid either by bidirectional brushing or ultrasound does not seem to make much difference. @whart has most of the bases covered the only problem I see with his system is that the KL Audio reuses it's fluid. It does pass it through a filter which will pick up particulate but it will not remove substances that are dissolved in the fluid. Fortunately vacuum drying removes most of it. The KL Audio by itself is not satisfactory. Any system that uses an evaporative drying method like blow drying is not satisfactory. The water evaporates but most everything else does not. I think the KL is the best of the ultrasonic cleaners and the Keith Monks is a great vacuum dryer but the whole affair takes up more space, is more complicated and takes much longer to clean and vacuum both sides. 

As for Walker Audio, Lloyd came up with a landmark turntable but the people around him turned the company into a tweak outfit in the worst way. I am sure he is rolling over in his grave.

Record cleaning fluid is a big can of worms. Distilled water is safe. Some additives may leave a residue on the record. I have begun to believe this is not a problem as long as it does not build up on the stylus. In some instances it may actually be of benefit but I am not sure....yet. 

@lewm , If Lloyd is responsible for the junk Walker Audio sells then my esteem for him has dropped quite a few notches. Overpriced? Maybe. Stupid. Definitely. Since when is PVC magnetic? People, unless you are doing immediate back and forth   A-B comparisons you can not make a comment on differences in sound quality. The human brain is not equipped to remember what something sounded like. You can remember what you heard but not what it sounded like. You have to focus on one aspect at a time say background noise level and go back and forth comparing. It takes effort and sometimes special or more equipment to set these comparisons up so nobody does them. Men being men think they are the best listeners and assume they can make these comparisons playing one sample then down the line playing the other an make a meaningful comment. We can not. Not a single one of us can do that unless the differences are glaring.    

@lewm , look Lew, you darn well know you can find people who still think the earth is flat. What people say or believe in can be wildly inconsistent with reality. I just call a spade a spade and move on. I'm sorry if I am not diplomatic. As far as I am concerned, you are what you sell, nice guy or not. This would make Lloyd a snake oil salesman.  I always though he had no part in this but you say otherwise. People like Mark Dohmann, Rob Robinson, AJ Conti , JR Boisclair , Dave Fletcher and Edgar Villchur would never resort to this kind of garbage. These are they guys that push on the limits of audio reproduction and would never resort to this kind of crap.