TL

R
Technically a professional is someone who profits from their work therefore a newb with a 2.0MP camera phone with rubbish IQ could become a professional if he gets people to buy his work
But it is very unlikely as us humans are attracted to pretty and fluent images with bright colours
but a Canon 450D (rebel / Kiss) could easily be used for Professional highend industry work, the reason most "Professionals" use dearer camera's is, yes better Quality and more functions, but just for the fact that a canon 1ds II is like a trophy to say "i have made it in the photography world"
same with 5D II and 1dIII
a phrase that isnt, used enough is, it isn't the gear that makes an image it is the person behind the camera