Memphis is the largest hub for FedEx; Indianapolis is their second largest hub. Given the explosion of the air cargo business in this COVID era, I'm sure there is an increased demand to get people to/from these cities.
MEM-IND is a 381 mile, 1h30 minute flight. Keep in mind, FedEx has to pay their employees while they deadhead. The shortest flights I can find for a random date in September have an elapsed duration time of about 4 hours, connecting over a variety of DTW/ATL/ORD/CLT. Cutting that by 2.5 hours each way to a 1.5 hour flight is a significant 5 hours round-trip savings. I'm assuming most FedEx pilots flying the heavy metal (not the props) are making over $100/hour (probably a lot more) - even at $100/hr, that's a $500 savings in labor per pilot right there. Any ticket they buy for less than the cost of the deadhead adds up to a significant savings.
We don't move many crews between IND and MEM, contrary to what most in this thread seem to believe. Certainly not enough to justify 76 seats a day in each direction. I suspect that if this is driven by FX, rather than DL just hoping to catch some FX business, it's for essential corporate travel only.
Secondly, that is not at all how pilot pay works. Whether they have 1 minute off blocks or 5 hours off blocks, they are paid their contractual daily minimum; shaving off a deadhead connection between MEM and IND will have 0 impact on pilots' daily pay, as they're paid only for the door closed time which will rarely approach their daily minimum guarantee between MEM-IND. If this does anything for crew productivity, it saves time and enables smaller trips - and only if the deadhead schedules work for what you're trying to crew on the other end. Per diem is a negligible cost, at best, and far outweighed by the higher cost of the nonstop. The tradeoff is obviously time savings, here.