No, because mono out is part of the main bus. If you split the channels manually, you can use the selection of "mono" and "main" of each channel. You may want to have kick, the low toms and bass in your subs, which means 4 to 5 microphone splitters. Use the Low Pass Filter in the mono output to get rid of frequencies you don't need in your subs.
Another (and I think better) approach is using "aux fed subs". You send the signals for the subs through one or two (linked) postfade aux outs. This mix will then follow the main mix and you can additionally adjust the individual levels as needed. Unfortunately the aux outs have no Low Pass Filter, so you need a crossover or controller to get rid of the "non sub"-frequencies. It is also possible to manually feed an aux out back to a channel in your mixer and route this channel to mono out. This allows you to use Low Pass Filter on a (mono) aux.
Just try what sounds best in your ears. I think for live music aux fed subs are the better choice, because they make the sound follow the music.
