The weather in October is very temperamental. It could be in the 70s or it could be in the 40s. Usually I would say the days are 60s, may have some days warmer and some cooler. It also depends if you are going in the beginning of the month or the end. I have seen it snow in Oct. I lived in the area for most of my life until I went full time in 2001. Haven't been there in Oct since then so someone else may have better recollection of Oct temps.
If you are talking about the Highmeadows Campground just up the road from the park I have been in part of it but never stayed there. It seems like a nice park and I've never heard anything negative about it.
Are you aware Hershey Park closes the end of September. It is actually only open weekends in September. I believe the last 2 or 3 weekends in October it is partially open with a Halloween theme then does the same through Nov/Dec for Christmas.
Have a good trip.
2007 Winnebago Journey 36'