There is nothing particularly unusual about using a mix of gaseous and liquid fuels in older industrial GTs that were designed for such operation. (I'm not so sure about newer, high efficiency GTs.) The burners and control systems need to have been designed to handle both types of fuels simultaneously. Most likely, there may be some modest efficiency variations along with the differing fuel mixes, and satisfying newer emission regulations could get to be more than a bit interesting. In general, the heavier the liquid fuels, the more likely there will be nastier problems. The more the liquids and gases vary in their composition, the more flexibility will be required of the burner and control systems. Most likely, there may be some variation in maximum load capability depending on the fuel mix. Fuel cleanliness will always be important for both liquids and gases.
Based on experience with a couple of troublesome units, I would want to be assured of a very extensive array of individual exhaust temperature measuring devices (thermocouples or RTD's) around the entire exhaust annulus to assure truly uniform distribution of the fueling and firing to avoid damaging hot spots. Averaging of the individual measuring points is fine for control purposes, but the individual points must be monitored continuously to assure proper operation.
At the very least, this should be a very interesting project. Since part of the purpose is to make good use of otherwise "waste" products, this should be carefully included in all performance and emission considerations. It may change all of the rules and criteria for the project.
Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.
