Can a headset base spacer ring be removed?
The tapered spacer is usually for water proofing the headset (dust cover), you can remove it as long as there is enough pre-load tension when assemble back the stem.

It is actually quiet useful to keep all the dirt and water away, especially if you leave the bike outside the rain. There usually is a set of O-ring(s) inside to keep the water dripping down the steerer tube.