I'm very interested in all those readings of "gresse" and have done a little digging. E.V. Gordon, in his notes to the Oxford edition, (p. 46) appears to assume without comment that the correct reading is "grass."
One online Middle English dictionary gives only "grass" as a definition for that spelling, and
another one only lets me search a truncated form and gives yet a fourth definition. So I have yet to find any warrant for "grease," though it doesn't seem impossible. When all is revealed, let's talk!
But what's more important: yes, great commentary. And what a contrast between today's two poems--the very accessible and the almost inaccessible without special aids.