Yes, they do specialize. At least most do. The organization you are writing the grant to may be able to refer you to someone in that field who writes them. Or some organization that has already received a similar grant may be able to refer you. Or there may indeed be someone local who can work with you. I have read/approved grants, written them myself, and taught grant writing to librarians. It is a fairly straightforward process and there are online resources to help. The Foundation Center in NY has good, reliable, clear online training and help. The larger the grant the more likely it is that you'll need to hire someone.