Jbosco is right here. While it may work well and still sound terrific, this is a less than ideal solution. Unless there are only two speakers on sticks, there will be a crossover/processor handling the signal to the stacks and subs. Plus the signal will certainly pass through some sort of house eq, and/or compressor. Patching directly out of the board or using turn-arounds on a house snake line would bypass all of that. Someone else incorrectly mentioned that only "powered" systems will pass a signal. Any sort of monitor with a thru pass feature will work, it will just pass what it was sent down the line.
Any good taper wanting to make stage tapes, should carry a pair of cable turn-arounds in their bag. But, even better is to be friendly with your resident sound engineer and have them run your stage mics through the house snake and back to the board, where you bypass the board completely and power them down the snake with your favorite preamps, while also taking his 2-mix (pre-crossover/room processing)