It does seem FISHY in some cases, and I wouldn't be suprised if some people have tried to or managed to cheat at this FUN contest, however, in the end I do not believe that these FEW people are swaying the votes enough to ruin the fun of the contest.
In the end one major reason I imagine that SWF.com has for this contest is to attract interest in this site and thus getting more customers. So new members, who join to participate in this contest, are probably thought of generally as welcomed new patrons atleast until there is reason to suspect that they are something else.