Im new to Surfski but I've been paddling at a high level in whitewater for the last 20 years (just to give you an idea of my experience with basically every combination of drywear that exists). Looking at the level six breakwater bibs, I don't see that they have a tunnel to mate with the tunnel on your dry top, meaning I cannot see how you would have a dry connection. They look like level six' take on a wader, which will not keep you dry even with a dry top. It will limit water intrusion, but I can tell you that you do not want water to fill up those waders. The dry top/drypant combo is what a lot of whitewater beginners will use to save some money and get, basically, a drysuit. However, the mating between the pants and the top should be seen as a safety concern, and must be done properly. If your pants filled up with water, you'd be in trouble for sure.
That being said, I'd recommend taking a look at the Kokatat whirlpool bib (https://kokatat.com/hydrus-3l-whirlpool-bib-with-relief-zipper-and-socks-ptuhwbr). It has a tunnel that mates with the tunnel of your dry top, and creates a near water tight seal between the two. Given the nature of a swim out of a Surfski, you'd have nothing to worry about. I've seen some beatings in whitewater where someone got some water intrusion into their pants, but Im talking about the equivalent of taking a series of waves on the head in a break zone.
Bottom line: find a drypant that has a system to actually mate with your dry top. I think level six should be more detailed about how that pant does not create a dry connection with a dry top. They do state you can pair with a dry top for "superior protection from the elements" which may be true for wading and fishing, but as soon as you start submersion, you're gonna have water intrusion.