The parking spaces at OKW are not numbered or anything for specific units. Every building has a parking lot, and in general, there are ample spaces to service that building, so it shouldn't be an issue.
We've never had a parking issue. Perhaps they may not get the space absolutely closest to your unit, but they will certainly not be walking 1/2 a mile either.
ETA-When we have had a guest come (myDSIL lives about 1.5 hours southeast of WDW) we usually call the security gate and let them know she is coming and give them her name. Not a requirement of having a guest visit, but we figure it smoothes the way.