There is no evidence we know of that he was.
According to Ian Fleming, James Bond "was a compound of all the secret agents and commando types I met during the war".
The most likely and primary inspiration for Bond may have been Ian Fleming's own brother Peter Fleming, who was himself a spy and carried a lot of traits later attributed to Bond. Others cited are the British intelligence officer Conrad O'Brien-ffrench, naval intelligence officer and avid skier Patrick Dalzel-Job, British spy Wilfred Dunderdale, the politician Sir Fitzroy Maclean, and even soviet spy Dušan Popov.
It is true that Porfirio Rubirosa, the most infamous international playboy of the time, had at least the womanizing aspect of Bond, if not the spy aspect (rumors notwithstanding). Born in the Dominican Republic, 'Rubi' quickly rose in the social ranks thanks to the help and money of the Dominican dictator Trujillo, who sent him as ambassador around the world.
However, Rubi became quickly known in the gossip columns for his playboy antics and jet setting lifestyle, not to mention his many high-profile marriages and love affairs. According to Truman Capote, it was due to the size of his sexual prowess.
He was married to some of the richest women on the planet, moved in political circles with people that included Fidel Castro, Adolf Hitler and John F. Kennedy, and is said to have had affairs with the likes of Marilyn Monroe, Ava Gardner, Rita Hayworth, Joan Crawford, Veronica Lake, Kim Novak, Judy Garland and even Eva Peron. His best known affair was with Zsa Zsa Gabor, one of the biggest actresses of the time, while at the same time being married to Barbara Hutton, one of the richest women of the time.
Rubi and Zsa Zsa
The question now remains whether Ian Fleming and Rubi ever met. While it is likely that they did move in similar social circles, there is no historic evidence that we know of. It is however very likely that Fleming knew and read about Rubi, as he was among the first celebrities to be famous for being famous (it should be noted that ironically the first person to be labeled as being famous for being famous was Zsa Zsa herself). But whether they actually ever met in person is unknown. The Dominican writer Isabella Wall noted in her Rubi biography that in her research she had come across FBI documents that claimed as much, but beyond that little is known.
While technically possible, there is no hard evidence, and like many things about Rubi's life, it may just be hearsay at best.