Hi Roni;
No it is not based on Buk per se, but I can see the pitch going like this:
"The main character is a writer, a bit like Charles Bukowski, but he is young and rich. He has sex with lots of women. He drinks. We'll call it "Californication" to get those Gen Xers that know the song from the Red Hot Chili Peppers... and it stars David Duvhovny."
Also remember that when he was out promoting this show on TV talk shows before it came out, he actually mentioned Bukowski by name. Coincidence? Maybe. Maybe he had started reading Bukowski when he was told that the character was LOOSELY based on him.
Hollywood has very few original ideas. By Hollywood standards this is a somewhat original idea. They usually just rip off shows from other networks or from the BBC. I'm sure that everyone remembers the rush to rip off Survivor, followed by the rush to rip off Who Wants to be A Millionaire, followed by the rush to rip off American Idol (even to the point that they have the EXACT same style judges; (Hip young judge, sympathetic woman (always sitting in the middle), brash Brit). How these people can sleep at night when everyone in the world sees them as unoriginal, sad little people, I can't figure out. I guess the money helps.
I don't think that they based it LOOSELY on Buk becuase that would make a hit show. I think that one of the creators was probably a fan and used Bukowski as a slight inspiration for the character. These ideas do not usually fall out of the sky.
Except for TinTin. That idea fell from the sky.
Bill