Yes, they can. They can see a reasonable guess of what the tip was added to the order. We can tell if you didnt add one at all, or if its in the $3-$5 area. So if your DoorDash order isnt getting picked up quick, most likely they know you aint tipping (or tipping enough). With DoorDash, the driver has the option to decline if the pay is low, and believe me, if you aint tipping, im not picking up that food.
UberEats is the same way. Just about a month ago (at least in my area) they started showing the amount with tip up front.
Just a fair warning if you decide to not tip for the driver to get your food. The healthier the tip, the faster that food will get to you.
Some people change the tip after the food is delivered or in route, no?