Re: self bailing boats
Offshore boats are typically those as described: Scuppers, high deck, ability to drain. The exact layout, size, height and even the types, location and number of scuppers mean they all perform differently.
Smaller, self-draining boats might -- might -- actually have their scuppers (some or all) below the waterline unless the boat is lightly loaded or underway. Seems to be less of an issue as boats get to 24' and bigger. These are generalities; exceptions to be expected.
So, having scuppers does not by default make it safe, but it's on the right track. Scuppers are best when fitted with some type of valve to prevent backflow for the reasons mentioned above.
In the end, it's all about a water test to see how a given boat's total package performs.