Doesn't seem right to me- It's one thing to buy a gift for a dom (or a sub) as a token of respect, affection, esteem, whatever; it's also one thing to pay for the services of a professional dom or domme, I can even understand why some people might buy gifts for a professional as a form of tip. That's all fine and good and lovely.
But for the only real interaction to be financial, the relationship goes (from my perspective) from being symbiotic to parasitic, if you'll allow the biological metaphor. Honestly, no offence to any specific person, but I kind of find the idea of these paypigs to be a little bit pathetic- a step even further down from the repressed, argyle sock wearing wannabe m-sub you find caricatured on dirty postcards and the like.
But you know- that's just my inflammatory rhetoric.