Good News! We've got the apps to work together! There's one small thing to note though. Product Upsell offers will only work if you have your recurring options set to "Multiple Products" or "Recurring Cart" mode (the two highlighted below).
The reason it doesn't work with "Single Product" mode is that if you have that selected, the customer never actually goes to the the Shopify cart. They go straight from the product page to the Recurring Orders checkout. So the Product Upsell app does not have a chance to see what's in your cart to make the proper offer. With either of the other two mode options though - you're good to go!