You might find that the Adult NP will limit you. If you want to work ER, unless it is a big city with separate adult and peds ER, you won't be able to see kids, which does limit your pt population. However, yes, you can certainly work in the hospital. Much depends on where you live and the general APN job market.
So, therefore, if you are in a big city like New York you won't need to be an acute care NP to work in the ER? I'm currently transferring to the ED while going to school and was debating whether to study for adult or acute care NP? My hospital's tuition reimbursement covers most of adult NP education but because there is shortage of acute care programs, I'd have to pay for a good portion of my education