It really depends on what park and time of day. For the most part, it will be easier to just go directly to the correct parking areas for each car and meet up. Especially at opening when there are massive amounts of people parking and moving around. CM are pretty much directing regular parking very strictly and it would be difficult for those going to HC to pick them up. It really is not that difficult to meet up from the parking lots especially if you do this before baggage check. (Follow the blue HC line along the edge of the road to get to HC.)
Epcot/DHS: Unless regular parking is extremely far out, these are easy walks to meet those in HC. It would be easy to meet up at the edge of the parking lots. At Epcot, it would be before crossing the road to get to where the tram drops off and at DHS, it would be before going past all of the bus drop off/pick ups. If they use the tram, then just meet at the tram. Who ever gets there first just wait to the side for the others.
AK: This is one where you need to park separately. I missed the line directing me to HC and had to exit the parking lot entirely and go back through the booths again. I would suggest meeting where the tram drops off here if you do not find each other before.
MK: Since you have to use the ferry or monorail from TTC to get to the MK from the parking lot, it is easiest to meet. Those in HC have a decent walk to the TTC entrance and those in regular can easily use the tram. When my sister was using an
ECV at MK, it was easy for her to drive up to the TTC, but I had to walk and I was quite tired that morning making it kind of hard. This is a parking lot that if you are not using any WC/EVC it might be best to just park in the regular lot and use the tram to TTC. Just figure out before if you think you want to use the monorail or the ferry and meet near the entrance to that transporation if you do not find each other first.
If you are going later in the day and they are not directing traffic or there is not many entering the lots, it might be an easy pick up of those in regular lot. Just note that sometimes the HC lots are full later in the day. I have twice not been able to park in HC at DHS with my sister and once was by 10 am.