LCO could be used as torch oil. Fresh feed (VGO) is other alternative. We have an FCC unit operating at very low severity that operated in the past burning torch oil in the regenerator in a routine basis. We used both LCO and fresh feed (Mild Hydrocracker residue) as torch oil.
Some important properties you may consider for torch oil are calorific power (the higher calorific value, the lower torch oil rate would be needed) and metal content