I would really advice to use a flash-meter to measure the lights and to get the ratios correct. (the ratios are important to document, should you need to set everything up again and repeat that light).
- you also have control and consistency over what you are doing when you are using a light-meter to gauge your flash-outputs.
Using a DSLR is a very convenient way to determine and fine-tune your ratios and angles, this isn't "cheating" either, as most photographers during the years used polaroids to gauge exposure, ratios and angles of light, since polaroid is more or less extinct, I think it's only fair game to use a digicam in it's place.
When I do this, I still think "zone-like" though, because dslr's are more like slide-flim (expose for the highlights, not the shadows), so after setting everything up, you need to start thinking how you will develop your film and how you will end up printing, to decide where you will place your (BW) exposures.