Yes, Thermal grease allows heat to transfer better by filling in micro sized divits in a chip.
thus giving a perfect surface for heat to transfer, any time you are applying a HS to a chip use thermal compound.
and if you want even better lap your HS and chip, but when doing the chip be very, very careful. if worried about ruining your chip at least to the HS so it has a better surface for the compound to seal.
-L_P