Well, in-game teams can be defined as teams used in-game as a whole, not just in Battle Tower.
Some of the in-game teams are used only for Battle Tower, but some others are used for battling in-game trainers. I know that in-game trainers sucks, you can even defeat them with something "stupid" (like lv 100 Charizard with all fire moves vs a Magcargo, and defeat that Magcargo with Blast Burn) but there are people who want "perfect" Pokemon even if it is just for in-game, and that's what the IGRMT section is for.
So basically, besides pure BT team, we In-game raters also rates teams that are purely for in-game (as a whole, not just Battle Tower)
If you have more questions or you didn't understand what I said (I hope you understand, actually
), feel free to ask again here.