I’m pretty sure I’ve done this before although majority of the time I do OLCI domestic because I’m bored or have bags to check or especially if I think I’ll be a bit late (I got the impression it counted for something one time I was really late and was questioned about OLCI). As long as you have your mobile boarding pass I think  you’re good to go with domestic and that comes up on your phone even without checking in. If it’s a day trip I definitely arrive later than 30 mins prior to departure.

I also remember reading others experiences about forgetting to check in for flights yet still boarding domestic  but I’m struggling to find the reference.