It's not impossible to successfully breed them without a brumation (cool down), but my experience is it does effect the size and fertility of the Clutch. If you have the ability, then I suggest you do it. It also saves on mice, and gives the snakes a break.
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Disclaimer: I do keep several snakes in pairs, and some in groups. However I realize that things can go wrong, and I have to keep a close eye on those groups, to be sure they are not being adversely affected by these living conditions. Also if one happens to eat it's cagemate, it is 100% my fault, and I know the risks in advance!

What's wrong with using CAUTION?!?!?!
King Snakes! Who can make a better mouse trap?
~ Jorge Sierra www.SierraSnakes.com