I'm just wondering here, but why do you think breeding is stressful?
Frogs, reptiles, tomato plants, what have you breed or reproduce because it is instinct nature for them to do so. I'm not saying that some frogs might not get a kick out of breeding (having sex) like humans do, but they mostly breed because it is in their nature.
Not that breeding might be stressful at all, but it happens all the time in the wild. I know that African Clawed Frogs breed or can breed up to 4x a year (every 3 months). As long as your frog or toad is healthy I don't see any problem with breeding.
I even wonder if not breeding as much as in the wild can harm them too? I mean if a ACF can breed with a male and lay eggs in matter of hours she obviously has eggs ready to go. Normally she lays those eggs every 3 months or so. In captivity she might not even breed at all, could that affect her? Idk.
Not trying to cause a ruckus, it just passed my mind. I don't think breeding is some super stressful period of their lives.