Hi ckm312.
Welcome to the HP Forums! You can still use the Officejet Pro 8500 with Mavericks (10.9) but you won't get the full features. You can print normally but you will be unable to scan directly from the printer. You will still be able to scan but you will have to do it through another method. I have included a document below that will show how to scan in 10.9.
http://h10025.www1.hp.com/ewfrf/wc/document?cc=us&lc=en&docname=c03967506
Thank you,