I think they can, but it's heavily contingent upon D'Antoni seeing the light, them developing or netting a quality backup PG, using a Marion/Amare/Skinner frontcourt much more often and sustained health and energy from Nash, Hill, Marion and Amare, of course is heavily dependant on a backup PG and Skinner being used more.
They can, but D'Antoni is the lynchpin. If he pulls the same he's been pulling, then the whole playoffs fall apart for the Suns.
However that said, if they hadn't sold off Thomas and Jones I'd be much more upbeat about their chances, which, as of now, I say is 40-60. With Thomas, Jones, Hill and, maybe, Skinner, I'd say it's easily 50-50 and maybe even a slight advantage to the Suns.