We must get the rotation of the source object, because it's more intuitive for the user to scatter exactly the geometry that he is seeing on screen. In Max the objects may have multiple transformations applied: you see a teapot on a table, but internally the mesh may be rotated in any angle.
There are multiples ways to rotate the items in Forest, without modifying the proxy:
1) Apply a Z random rotation using closely range values, as 59 to 60 (don't use the same value since Forest will disable it).
2) Swtich to Custom Edit mode and edit the rotation of each item individually.
3) You can even rotate the full Forest object, although the result is different because the pivot used.