As long as it's presentable and clean I'm fine with whatever
I know of a couple of guys who do take really good care of their hair though(they're straight). They deep condition regularly and use moisturizing shampoos and conditioners, mostly cause they're surrounded by girls(sisters).
I don't expect that though. Due to my curly hair however, I do take care of mine
It all depends on the guy. If you are the type of guy who can roll out of bed with messy hair and still look sexy with it then no, you don't need to style it at all. Other than that, yes a guy's hair should be kept well and not necessarily in a style, but groomed. Styling is a major plus!