Appearance is where the similarities end with those ports. They are wired completely differently. You probably wouldn't break anything, but it also wouldn't work, if you managed to get that mouse plugged in.
If you have one of the G3 PowerMacs that was pre-USB based mice and keyboards, then you either have to get an adapter or a new mouse. eBay is an excellent place to track such a thing down I might add. You could also check with any local schools or universities. They might have a few stuffed away in a drawer or closet somewhere they'd let you have. At my last job, there was a whole, rather large, filing cabinet devoted to just storing odds and ends for computers. One whole drawer was devoted to spare keyboards and mice. Some larger schools will have regular sales where they allow the public to buy old equipment they wish to dispose of. There are plenty of options if you know where to look.
Was able to buy an old MAC and want to learn. The mouse is very hard to operate. It's a Power Macintosh G3; Sony monitor and Apple Desktop Bus Mac2 mouse; apple keyboard. I have an old Microsoft NEC mouse. Can I use the NEC mouse for the MAC. The connection looks the same, but scared I'd destroy the whole thing. Will appreciate any feedback. Thank you.