What GPS program is that on your ipad? EDIT: I see after doing some web surfing that appears to be part of the DeLorme/MapShare feature.
Leads to another question, does your ipad need cell service or can it stay up to date by syncing with the DeLorme by bluetooth or some feature?
Regarding the App:
It is Motion X GPS HD. I chose it because you can enter URLs for online map tiles, and then preload those tiles for the area you're traveling through. No other app that I could find allowed this and I wanted to load Forest Service maps with much more road detail. CalTopo shows Forest Service maps so with a little code searching I found the URL to use in Motion X. I'll find it again at home and post later.
Regarding iPad service:
Any cell plan enabled iOS device can use GPS outside cell range, but isn't able to load maps outside cell range. You can select an app that allows you to download maps via cell or wifi before you go.
Regarding InReach pairing:
According to the info I could find, all iOS devices can pair via bluetooth and then piggyback on the InReach GPS. But I couldn't figure what settings were needed on my GPS enabled iPad to make that work. So instead it used it's own GPS. It was very accurate and the signal was consistent. The only nitpick is that I had to keep a close eye on the battery.
Regarding MapShare:
For mapping and track recording, this doesn't perform with the same level of detail as a traditional GPS unit or Motion X (here is the route as published via MapShare:
https://share.delorme.com/kevinmeyers). But for communication, it was great! DeLorme has an app called Earthmate with all the comm features built in. Texting is as easy as browsing your contacts on the iPad and looks very close to any chat/text interface. And on the MapShare site link you can see that visitors can also text me, ping my location, or drop waypoints to me for suggested stops.