Nope, you can close the others without talking to the count of Skingrad. In fact (spoiler - highlight)
closing all the gates outside the cities is not a must, you could just go on to do Martin's quest. But closing them will benefit you later on. Plus those sigil stones can be quite nice.
As for the count you might want to check out (spoiler - highlight)
his vampire lair, which is where I found him
Hope that helps!!