Once again I'd have to disagree that BullMatcher 1 would be in danger of overtraining if he added some supplementary cardio/strength training to his routine.
I still very much disagree that your training should be your only source of cardio training. Now, in the begginning stages of training yes, that's a very realistic approach, as the begginner's body simply won't be able to handle the training volume.
However, BullMatcher 1 has been training for 3 years. There's a big difference between someone who has been training for 3 years and a newbe.
When I was training seriously, I went to 3 (sometimes 4) 90 min (which generally turned into more like 2 hours due to sparring after class) classes per week, performed Shihan Lysak's C.R.A.W.L routine at least twice a week, and then would occasionally have a belt test thrown in (the shortest of which was 2 1/2 hours of the hardest workout I've ever experienced).
My training partner far exceeded my stats however. He did everything I did (3 C.R.A.W.L workouts per week instead of 2), would throw in a workout consisting of 10 sets of 10 clean and presses, would come to the gym up to 2 hours before class and grapple, and would go train at my instructor's brother's school whenever he got the chance. His cardio was incredible considering that he hadn't even been training for 2 years, and his strength was also incredible for his size.
So, to suggest that adding in a couple of cardio/strength workouts per week is going to lead to overtraining, is in my opinion most certainly not true.
Now, if he were indeed doing 2 hours of Muy Thai every night, yes, then adding in supplemental workouts might be a bit much (at this point anyhow).
I would agree though that technique is indeed an essential piece of the puzzle. However, in my opinion that is what class is for. When do you think it's more likely that he will have a competant and willing training partner with which to practice his techniques; in class, or out of class? Most often the answer is the former.