Hi John, I tend to prefer things to go together, whenever possible, for the sake of continuity and professionalism but I'm not entirely sure it's *that* much of an issue overall aside from personal preference.
I suppose, if it's not at all possible to get a domain that reflects your business name and you don't want to reconsider your business name then it's best you design the website with the business name in mind - after all, your business name is your brand, not your URL.