SSkim,
UCG syngas production does produce a reasonable amount of CO2 along with the usefull bits H2 and CO. It is the particulates that are left underground. In the case of CNX there seems to also be a high percentage of CH4 and C2H6 which will also produce CO2 when combusted.
So, unfortunately, CO2 as a result of syngas production and usage will still have to be sequestered.
P