I had a serviceman connect my gas stove/range back up to the gas line. When I asked him if he used teflon tape or liquid pipe dope he said neither as my compression fittings was a type that did not need it. I was not aware there was such a compression fitting. The gas line does not appear to be leaking at this time but could it begin leaking at some point in the future?

Is the connector made of smooth copper pipe, or is it a pre-made flexible connector? Flare fittings do not require any thread sealant, because the flare is inside the fitting and the gas doesn't reach the threads making any sealing compound useless, giving false hope of protection. On the other hand, most flare connections require the flare fitting to be screwed onto regular black pipe, which would require a thread sealant. I usually use teflon tape for water connections and teflon paste for gas connections. If there are threaded connections that were sealed before and not disturbed, chances are they are still sealed. If all he did was disconnect and reconnect the same range, he is most likely correct. With that said, it's your house and it's your range and it's your life. If you are not comfortable, you should be more than welcome to contact the servicer and ask for further explanation, assuming he charged you a fee for the service he rendered.

If you read the instructions on the flex connector it states NOT to use any tape or sealant.