I will preface this by first stating: I'm not up on PDGA rules.
That being said, I don't care how you "throw" the disc as long as:
1) It's launched from: the designated tee box, original lie, or customary 1meter relief; whatever is applicable to the shot.
2) It is launched without any mechanical device and totally powered by the player.
3) Is an otherwise legal throw (i.e. follows any mandos, doesn't go OB, etc).
People use all kinds of "unconventional" throwing styles. As far as I know, none of them are illegal. IMHO, you could spit it out of your mouth, or fart it out your butt, it would still be legal. Just don't expect me to hand you your putter out of the basket
.
If someone was on my card during a tourney, as long as they met the above criteria, I wouldn't even think of reporting them. If it violated some section of the PDGA rulebook, and came under scrutiny, I would have to seriously consider the intent of the rule and might even lobby to the TD on their behalf if I genuinely thought their method didn't result in some sort of unfair advantage.