Best to have, yes. Whenever it is the event prior your wedding day celebration or after it, a beach party is better with music .
Choose the style of music you prefer to hear, having in mind the venues, and beaches owners usually have some great DJ to recommend that know the ambiance to provide.
Some couples think of having a live band for a beach party, and rare to mention, I would not recommend it. It is an outdoor chill-out event, where mingling is key. You want your favorite people to chat together, to meet new members of family or friends. I truly think having a ban there can kill the purpose of your beach-party.
If you have your beach-party prior your wedding : focus on interactions between the people.
If you have your beach party after the wedding : focus on a time-framed event where people can join when they’re ready, before they have to leave the area. Focus has to be done on a chill-out ambiance.
In the two cases, the live-band musicians won’t receive the recognition and attention they deserve.