The short answer
Yes. At Erg Chebbi most camps can bring you in by 4x4, which takes a few minutes instead of a long ride. Agafay camps are reached by car anyway, with the camel as an option. Erg Chigaga always involves a 4x4 over piste from M'Hamid. The camel is the classic arrival, not a requirement.
In more detail
The 4x4 is the practical choice for young children, travellers with a bad back or limited mobility, and anyone leaving very early the next morning. Our camp guides say we arrange whichever transfer suits each guest, and our desert tours include both options.
You can also mix them. Some guests ride out at sunset for the photographs and come back by 4x4 after sunrise, or the other way round. Another option is to let the rest of the group ride while one person goes ahead by car with the bags.
Inside the camp you walk on sand, which is soft and tiring. If walking on uneven ground is hard, say so when you book: some camps are flatter and closer to where vehicles stop than others, and the tent nearest the dining tent makes a real difference after dark. Agafay camps are the easiest of all: you drive almost to the tent, and the camel ride is an extra you can take or leave. For Erg Chigaga, the 4x4 crossing from M'Hamid is part of every trip, so the camel there is always optional.