The ceramic ring around the contact is more of a heat resistant support for the contact than anything else. Atleast that's what I think its main purpose is, keeps the little contact straight and rigid. I asked this question here on RC and was advised not to use the bulb. This was an old bulb, given to me alonmg with several other old bulbs so I did heed the advice.
If it were new and I couldn't get it replaced, personally, I probably would use it anyway.