Poly and bdsm in any ratio can be healthy. Communication was already mentioned so I won't dwell on that.
What I will dwell on is the importance of separating the two emotionally and intellectually. Poly is not bdsm, bdsm is not poly, and it's important to understand the details and intricacies of each, in and of itself.
Inevitably, you will stumble over something at some point. Everyone does, both in poly and bdsm. No one is born an expert in both fields. You learn through experience.
So it's important to have as much information as you can get about both poly and bdsm. It's important to know what kind of activities are poly (eg. dating another person) and what kind of activities are bdsm (eg. gangbang). Then when problems happen, it's important to analyze: what parts of this problem are within polyamory, what parts are within bdsm, and what parts come from combining the two?
Personally, I would probably pick one to focus on first, get comfortable with it, and then explore the other. That's just how I would do it, and not necessarily a recommendation on how you should do it. But that approach has two advantages. First, if you have an issue right away, you know exactly what the issues is from. Second, you get to spread out the discovery more... Sure, you can have an explosion of polyamory-bdsm... but where do you go from there? If you spread it out, you get more explosions. There's a limit to how awesome one experience can be; eventually you reach a point of diminishing returns.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker