After viewing a couple of YouTube videos on packing steering head bearings, I'm not sure a grease fitting will do the job. Absent a tool that forces the grease into the bearings, most people put a big gob on the palm of one hand and press the lower side of the bearing into the gob, rotating the bearing, repeating until the grease appears to ooze out the top of the bearing.
So I'm not sure that merely squirting grease into a Zerk fitting would really "pack" the bearing, but would probably just force the grease up into the steering tube between the upper and lower bearings where it wouldn't do much good.