No. Zen Bathworks Cedar Hot Tubs have wood-on-wood interfaces that seal because as the wood absorbs the water, the compression retention bands channel the forces on the staves (wall pieces) and floor toward each other to create water-tight seals.  As for the fittings, gaskets are supplied to seal their interfaces with the wood of the tub. Therefore, no sealants are needed besides the PVC primer and cement used to join the plumbing fittings and piping.