Mostly I lurk, but thought I could add a little here. Years ago I trained in IMB Cincinnati under a guy who was certified by Bustillo (Elden Clem). When you joined the gym, he made you get an ABA card. He also pushed guys to have at least one fight as a boxer if they were going to hang around (I had already had kickboxing matches, as well as training and sparring in boxing gyms, so I passed). Richard backed the idea enough that he asked Elden to use the IMB name. At least at that point it was the only "IMB" affililate using the name. I have to say the guys there were pretty good fighters and the focus on boxing created a base/approach that today would be described as "functional".
Related to that, I met Elden through Rafael Lovato (who is now a Machado Black Belt out west). Rafael was also boxing based (having fought as a kid). I did a lot of private work with Rafael and know that during that time boxing was really the base he used to explore everything else. In fact, when I asked to learn trapping he told me to get it from someone else because he really was not into it. Again, Richard certified Rafael and clearly supported the guy.
Finally, here is Boston there is a Bustillo related gym that also teaches pure boxing classes (and pure Muay Thai) classes. They have trained golden gloves champs in the state.
All of that leads me to believe that boxing is a big part of the influence for at least some people in his organization. Of course, it is important to realize the Richard boxed as a kid, before every meetign the JKD group.