Will Oracle scan your tickets on my phone?

Yep, they will. Got mine through Ticketmaster mobile website and had no problems at entrance.

Yes

Yes. If you anticipate any issues with your cell service or wi-fi, try to save a snapshot of your QR Code to have it handy for scanning at the entrance. And if you originally had hardcopy tickets from Ticketmaster mailed to you but can't find them, you can try transferring the tickets to someone who'll then Transfer them right back to you. Now they'll be available as eTickets for scanning on your cell.

Most definitely

Depends if they send you e-tickets. We went to the Scorpions last week, and they only had paper tickets. Just check first with the promoter (who you bought tickets from)