Absolutely fine, the designation is just for motorised infantry. And then again, there wasn't always the motorisation needed or desired in 1944 when you're retreating towards the Rhine! The TO&E for the period we're talking about was slightly different at platoon level which is why we box the troops with smocks as SS Panzergrenadiers even though they have no overt SS insignia. So, you can use either as normal Heer panzergrenadiers!