You can do it, but keep in mind the seat licensing, you must have an adequate number of seats available on the target system for the types of users you are bringing over. The licensing wont migrate; I don't know if they can still transfer licenses between systems; it would depend on your maintenance agreement and the age of the systems.
You'll need to create an archive with just the users you wish to move; and if there are any App Builder apps, you'll need to migrate them separately.
Good Luck!
30n30w