I wouldn't put it in the dishwasher. Temperature is too high, even if you air-dry and even if you don't use your dishwasher's onboard water heater.

Both Snell and CPSC standards for bicycle helmets require them to survive temperatures of 50°C (122°F), plus or minus 2° (Snell)/3° (CPSC). Tap water is ordinarily hotter than that.

Even considering the length of a single dishwasher cycle vs. the minimum four hours a helmet has to undergo the heat stress, this is a total risk/benefit analysis FAIL. Benefit: you save ten minutes and your hands stay dry. Risk: catastrophic head injury.

And that's disregarding the potential effect of dishwasher detergent on the EPS. I don't know whether chlorine bleach (or oxygen bleach, if you use a "green" detergent) degrades EPS or not, but it's generally a bad idea to expose a helmet to any harsh chemicals.