Hives do like heat..and therefore, the fever could definitely being fueling the hives on... Whenever I have gotten hives, which can take awhile to run their cycle (for me, several months) on and off.. I drank lots of water to help flush out my body.. Additionally, I limited any medications as in my case, it seemed that asprin could provoke the hives.. as can sugar and a myriad of other things. Also bear in mind, STRESS<<<< that is what really did it for me... so yes could be the fever does aggravate the hives and vice versa. Don't forget, being physically sick is a form of stress on the body...
I found Hives to be a vicious cycle... you may have noticed that they become worse at night? For me, it's when I was snug under my covers that the itching would begin.. why? because of the warmth from the blankets.. Therefore, I had to make sure I was using ALL cotton sheets, light clothing and when bathing, the water could never be really hot... more like tipid.. By doing all of the above, it helped soothe the hives and they eventually went away..