IMO the biggest concern is HOW MUCH you dump at a time in one spot and how many others are doing the same.
Say you have a 40 gal grey tank and dump every 3 days. Now, add 10 other campers who are doing the same during the same time frame. That's a LOT of water getting dumped in camp and will have an effect on the ecology.
In contrast, most tent campers are dumping maybe one or two gallons three times a day. That is only 18 gallons every 3 days and it isn't all in one go nor all in one place. The water has time to soak into the soil and dry out before doing it again - even if all the tent campers are doing so.
My FnR has an 18 gallon grey tank. Cassette toilet. If needed, I will dump the cassette into the campground toilets. I have a 6 gallon grey tote - if needed I will ask the ranger if OK to dump in toilet or on the ground every couple days. If no and there is no dump station in the area, then I will just keep my stay within my tank limits.