I also think instacart workers might be at higher risk of virus exposure because, as I understand it, they need to go into the store and pick out groceries - while food delivery workers only really interact with the food bag at the counter. I'm also not sure how often the different contactless delivery options are chosen, but instacart would include more exposure if you needed to hand every grocery bag to the customer compared to one or two food bags.
Source: https://shoppers.instacart.com/
Haven't worked as an ISS, but I presume that they have no say in their orders as they aren't paid per order. I actually have no idea if they even get a portion of tips.
source: have run for Instacart before.