If by valid you mean binding, the answer is probably yes. As long as the person signing on behalf of the DBA was a person authorized to grant the easement, the LLC will be bound to the terms of the easement.
The other question is whether there is clear title to the easement holder. The answer to this depends on how the deed is drafted. If the easement is granted as JC, a DBA of J&J, LLC, and J&J LLC is the record title holder, then title is probably clear. if the easement is simply granted as JC, then you may have to have a new easement signed clearing up the chain of title.
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