Maybe but most endowments actually have "legally?" bound or otherwise contracted uses in universities. Thats why Harvard can't just tap it's endowment to fund research the current Admin has cut. So I'm doubting that endowments are being used in this way to pay coaches.
Sure, but if an endowment is paying for, say, the football coaching staff, then that leaves that much more money free in the general fund to pay for other things.
If the endowment is paying for something that otherwise wouldn't be paid for generally, that's a different story.
This isn't really fair I think. Academic money is actually not fungible - it can't be used to fund athletics, and vice versa. Just because both pots are relatively large doesn't mean that the money itself is fungible.