Cyriacus
Senior Master
Can I? Yes. Will I? No; note, please, that I included the qualifier "that I have known." I rather doubt you'd know them. Not every skilled martial artist is famous. Though I do recall that Bruce Lee was reported to have won several cha-cha contests.
You seem locked on "you must do martial arts to improve martial arts." And this is true; you can't learn to punch or kick or throw or be thrown or what have you about martial arts without doing martial arts. But lots of things that are not explicitly martial arts can improve your martial arts. Obvious ones: strength training and cardio training. You do, I trust, agree that strength training and conditioning can improve your martial arts? So can other things. Ballroom dancing (or other forms of dance) has been discussed. It's not the only way to learn those things -- but, y'know, I can think of worse ways to learn than holding a pretty girl!
You also mentioned yoga, and I definitely want to address how yoga can help martial arts. Some types of yoga can help undo the damage and harm done to the body in training. Other types will improve your control and awareness of your body, and it's pretty clear that better flexibility -- especially when coupled with strength as found in many forms of yoga -- will have martial benefits. In fact, from what I've read, one art (kalaripyattu) doesn't even start martial training until the student has done a certain amount of yoga.
If anything, ill convey My View.
Where I Trained, we had Three Gymnasts, and one Dancer, over a period of a few months. Two of the Gymnasts dropped out after three classes, the other one couldnt get the stances right, and the Dancer was laughably weak, despite flexibility and footwork.
You cannot so much Benefit Martial Arts from these things.
Some Martial ARTISTS are Benefited, if they are Privy to such things.