Hello, Sr.com:
Is the use of digital backups on PS2 through OPL/PS2Loader legal? I do not know if running digital versions of any given game actually decreases loading times but I still would rather ask to be sure.
The game I am planning on running (Nano Breaker) has, at some point (I do not know when), been removed, so I could not ask the community directly outside of a runner who seems to be active on reddit but who has not yet replied.
What do you mean it “Has been removed” was it already a game before?
Personally, I wouldn't allow it but like Taru said, its on a per community basis. If there isn't a CD or DVD disc involved, it will likely have better load times over original hardware.
"USB loaded" (whether it's from an actual USB flash drive, an external HDD/SSD, or SD card). Tend to load much faster then when read from disc. As it requires a modded console and was not meant to be a supported/official way to play games, it would give an unfair advantage (ie: you'd need the best mods with the fastest media to have a competitive time).
Backup discs on the other hand, tend to read slower, hence why it is accepted on most leaderboard that are not too "purist" about their games. It sometimes still requires a softmodded console, but at least you're not playing at an advantage, but rather the other way around! In the same vein, flash carts will depend on their fidelity.
Same deal with emulators: Instructions and load accuracy, how competitive and accessible a game is, and the reputation of a specific emulator version will play a big role in whether it's allowed or not.
In any case, it's always up to a game's community to decide what is allowed or not. Hopefully these should give you a good idea behind the general reasoning why something is or isn't allowed.