Yes, in ANY vertical antenna, the ground pain (body of the car, the radials you lay out on a ground mounted vertical, those parts of antennas you see sticking out parallel to the ground on rooftop antennas) are as much a part of the antenna, and are as needed as the vertical part of the vertical

Interestingly, as you start to put out more and more ground radials, your SWR will go up to a point, because a vertical doesn't have a natuaral resistance of 50 Ohms.

All this stuff is 'old hat' to hams who have studied it (not all have) It's PART of the reasons hams have been known to be able to get signals through, we tend to know the issues. Unfortunately, a lot of hams today haven't learned. Hams USED to even practice getting on organized nets for 'traffic handling' - basically how not to step on each other, and get a message through