How much does park factor have an affect on fielding?  In a park like hilltop will a superior defense suppress the number of would be hits? And with a park like Safeco would defense add in giving up even less hits with a superior defense?

I don't think that park factor contributes to any more/less hits...only the ratings matter.

A superior defense in a positive singles park will certainly help to reduce hits as the park itself will promote more of them and the more + plays your defenders make will convert those hits to outs. A superior defense in a negative singles park will also reduce hits, but because the park is already helping to do this, you may not see as many + plays as you would in a positive singles park.

Sorry I meant the ratings not the overall park factor