Yes, absolutely. Builder’s representatives (salespeople) work for the builder. There are many factors of buying a new home that they will not tell you, because their loyalty lies with the builder. You should hire an agent that has experience selling new construction and has knowledge of new homes.
Yes, absolutely. Even if there is an open house, sometimes if you go without your agent on your first visit they will not allow your agent to represent you should you write a contract.
While you may think there will be added fees for you to have someone represent your best interest when buying a new construction home, it doesn't actually cost you a thing. Home builders want the REALTOR® to bring their customers into the communities they are building and are prepared to pay a real estate commission (out of their pockets) for them to do so.