Indeed, this function does not yet exist in the released version of polymake. But it only scales a matrix with the common denominator of the entries (without the first column, which is the homogenization). As long as you ensure integral input the gfan-function should work without it.
I'm not too familiar with the output our gfan-function should produce. However, on your input the rule returns a fan whose only cone is a linear space (note that MAXIMAL_CONES only returns the maximal cones of the pointed part, so in the case of a linear space, this is empty, i.e. just the origin as a pointed fan). Your input are the vertices of a simplex, so there aren't too many ways to triangulate.
If you input the vertices of a square you should get two maximal cones consiting of a single ray each.
