Yes, you can, but if every time you have to go somewhere new its not there its not really serving very well as your GPS, especially if you really need your GPS on a regular basis. At a minimum that means you need two GPS apps

I really enjoy adding stuff with street complete and wanna get more in the habit of it for anywhere I go regularly, but if someone needs to be able to get places and osm doesnt have the data they need, its totally reasonable for them to use a different gps- open street maps can't get them where they need to go, so theyre gonna need a different one

Personally I think if someone's needs are simply not met by the open source tool it is okay for them to look for something that will, even if the open source/free licence thing would be better in terms of freedoms

This would take dozens of hours though. If there were absolutely no option I would consider it but it is also absolutely useless for discovery: I have to already know it's there and add it myself. Every time someone sends me their address, I have to add it to OSM before I can navigate to it. That is a non-starter for regular, reliable use. If I just had to add something every once in a while that would be one thing, but it's entirely unusable.