It doesn't sound like he is severely dehydrated... Mildly, sure. That's to be expected.
DS came down with a mild case of Norovirus around 9-10 months. Didn't throw up much, but his intake went way down due to lack of interest as well as low supply since I was sick as well. We gave water, pedialyte, and minimal pumped breast milk as he would take it. I remember him not crying (unusual), being very cuddly but uninterested in nursing, sweaty but chilled/feverish, and producing minimal diapers.
We just waited it out. Most of the time these bugs are pretty short-lived. I wouldn't worry that much unless his capillary refill time gets longer than 3.5/4 seconds (press your thumb to his sternum until white, release, then count) or he stops producing tears/saliva.
Does your ped not have an after-hours number?