Yes. PSA has graded a few. Here is some proof:
56 Marciano (pop 3):
56 [sic, 55] Gavilan (pop 1):
56 [sic, 55] Moore (pop 1):
They are under "nonsport cards" and "multisport cards" in the pop report; try a player search instead.
I am not sure if PSA graded a 55 Marciano and labeled it a 56 as they did with the Gavilan. Though as Dave Hornish's research shows, they are all 55's, issued in two formats and two sizes for Marciano, one each for the Kid and the Mongoose.
I put a picture of the '55' trio on the back of my book's latest edition.