"I've got a customer that wants a smallish left chest logo on a sherpa (think of shag carpet!) sweater. I've seen somewhere where they do like a running stitch grid about an inch all around the logo to mat the item down (color thread used, matches the garment) "
Let who ever is doing the digitizing know that it is going on sherpa fleece. They should be able to make the required adjustments.(extra underlay) A lot will depend on the logo.
One thing to make note of, if you have lettering (under or around the logo) you might want to put a full fill box(or other shape) first with the lettering on top. Small lettering will for sure get lost in the fleece.