Volt-free is, in basic terms, an isolated circuit - you supply the volts! Some people call this 'dry contact'.
The meters pulse is simply relay or opto-isolator switching. As scopes measure voltage and there is none, you will read nothing.
Commonly in gas and electric meters, it'll be a N.O. relay.
You could place a coin battery or AA battery in series to a pulse output:
PulseOutputB------(+)Battery(-)----ScopeGND & ScopeProbe---PulseOutputA
Then you will see a voltage reading of the battery on every pulse!
I found a datasheet on a gas meter to get an idea:http://www.sontay.com/Datasheets/MG/MG-G.pdf