It is very possible that these two separate issues are related to a common issue. Cat's tend to get dermatitis under the chin, it can extend down the neck, can sometimes be in groin, or in the same areas of the dog. The cause can be any allergy, but fleas are a huge one. We often don't see fleas on allergic cats, because they groom very effectively, yet they can still get bitten triggering the allergic response. The crusts or scabs or bumps are bacterial infections, a lot like pimples.
The dog tends to get the lower back, tail head, and around the bottom with flea allergies. Thus far we can at least speculate a common cause that they would share.
Other allergies can also trigger these outbreaks, but it would be a little weird for cat and dog to share the timing.
Either way, your veterinarian should be able to treat with an antiinflammatory (often a shot in the cat called Depo Medrol that lasts a month at a time and a shot followed by pills for the dog) and antibiotics if needed.
It doesn't matter what the trigger is as far as treatment, but considering the flea as a possible cause, and this is the season fleas really begin to flourish, allows you to look at your flea control and decide if it needs shoring up. Sometimes we need more aggressive tools during the late summer and fall than we did earlier in the season. This is good to consider because we don't want to go to the vet any more than possible.
Some pets will get relief from medicated baths, antihistamines, or fish oils (omega 3 fatty acids) in the diet, but most allergies require medicine from the vet. It is more similar in them to when we get poison Ivy and we often get prescribed the same depomedrol but in a pill form rather than the shot.
I hope this helps and gives you a direction to getting them better. Please don't hesitate to ask any more questions if I haven't answered your concerns or need more specifics.
Thanks. Hoping the itching/skin issues go away quickly!
==== Dr. Will