I think that it is best for law departments to use the evaluation form that prevails throughout their company. Yes, it does not apply in many respects to evaluations of professionals, but it is better to stay in sync. Consistency allows HR to evaluate the pay and grades of the law department against the same distributions in other staff units (See my post of Jan. 23, 2006 about matching lawyers to their clients by grade.)
Some law departments prepare a supplemental page that has space for evaluations and considerations that are unique to the law department.