This does not seem likely to me. I found LANDAMAR (and LANDMAR and LANDEMAR)*, but not LAMAR.
Seibicke** doesn't list this variant either and says: "from the French surname Delamare"
*
Ernst Förstemann: Altdeutsche Personennamen (1906)
**
Wilfried Seibicke: Historisches Deutsches Vornamenbuch I-IV, 2000 ff.