Wapol his devil fruit is a paremecia, sea stone doesn't negate paramecia devil fruit powers. Sea stone only makes the devil fruit user weaker, Luffy can still stretch under water. If his power was a logia, then it would negate his devil fruit powers.
Personally I think Wapol could eat seastone, but it will make him weak.
Personally I think Wapol could eat seastone, but it will make him weak.