18 x 10J offset 65
 

Will rear porsche oem rim size 18 x 10J offset 65 with 18 x 285/30 tires fit on a 2001 boxster without rubbing?

No. You will need a spacer to make them fit. Something around 20-25mm.

I have 18x10.5 52et with 15mm spacers on 275/35 at stock height. I have about 3mm of room between the tire and the strut. I don't rub but the tires do stick out past wheel well, so if I want to lower the car I will need to roll the fenders. I think the 285's will be too wide and like John V said you will need spacers in the 20-25mm range to make the wheels fit. You may want to find wheels that are a better match for a Boxster.

i use a 21mm spacer on my rears that are 18x10 ET65. they're flush with the fender & don't rub either the fender or the strut.