First, I did not do a search for this answer.

I had to replace my iPad Air 2 wifi with a "cellular + GPS" 64GB.  I have Verizon accounts.  Is there a benefit to turning on Verizon service to this iPad, that helps with the Pilot App?

Thanks in advance.

Depends on if you want to be able to view maps while flying.  Maps come from the internet.  The internet gets to your iPad one of two ways.:

1. Wifi if you are close to a WiFi hotspot.  (Such as your house.)
2. Cellular connection.

It's possible to preload or "cache maps".  But if you want maps to load out on location... You might pay for a cellular connection.    Otherwise it would be a waste of money.

No GPS in the wifi model...

Sounds like a waste of money to me, unless you're going to be using iPad cellular data for a lot of other stuff. Why not just create a mobile hotspot with your phone? That way you're not paying an extra $30-50 per month.

I use my iPhone 6 w/ a hotspot connection to the iPad Air to download maps when I don't have another wifi connection to use.

If you are on a Verizon Family Plan, it only costs $10 month to add an iPad to your shared data account.  Of course, there's also the $40 one-time activation fee.  Real-time map loading will be your biggest DJI Pilot app specific benefit.  But you will now also be able to check weather, check email, post your favorite aerial photos to Facebook, etc., check the DJI forum for the latest posts, order from amazon.com and ebay, etc. all while you are out in the field.

Thanks gang.  I decided to replace the tablet I had on my Verizon plan with the iPad.  Not going to impact my use or plan at all.