It depends more on overnight lows. CAM cycles in highly thermoperiodic cacti rely on cooler nights for those stomata to open and gas exchange to occur. If overnight low temps stay up around 80F-90F, many cacti from thermoperiodic habitats just sit there and do indeed go dormant and really will rot and die if watered. I have lost almost all of the fatalities here in Phoenix from summer water for plants like Escobaria missouriensis, Pediocactus, etc. who need cooler nights.
Now, I check the habitat. Tropical or even subtropical cacti grow like weeds with hot nights and will take all the water you throw at them. All Chihuauan, Great Basin and generally montane cacti need to be relatively dry over the summer if the overnight temps are too hot, basically anything over about 70-80F. Sonorn and Mojavean cacti are more forgiving of hot nights and thunderstorms, an adaptation to their habitat conditions.
Sadly, I have found it really is this complicated.
However, if your nights cool off, no worries at all. Everyone will be happy, dormant or not. I have found that cacti watered during summer dormancy are just fine, as long as nights are cool.
just my .02.