Yes, you can use the same Extension List in more than one hunt group. Just know that there is a limit to how many phones can ring simultaneously before slowing down the system. From the help:
Adding a large extension list can result in slowing down system performance. Adding an Extension List that contains more than 60 members may cause a system slowdown because when the list is called, ALL members of the list are called at the same time.
When using an extension list for ring-in or hunt groups, do not exceed 30 phones per list. The system can send ring signal to up to 30 phones.