As far as I know BungeeTabListPlus does not support a Sponge build, but if it does, it would be up to the creator to use PlaceholderAPI, so I cannot say if it is supported.
As for reloading, the only placeholders I can add are placeholders that are internal to PlaceholderAPI. Any placeholders registered by other plugins, for instance Nucleus’ Gluon, cannot be added without a full restart yet. I am working on a feature that will allow them to run code when PlaceholderAPI reloads, but that will still require some time as the other developers would need to implement it.
EDIT: The internal statistic in Sponge for deathCount is deaths, so %statistic_deaths% is the working placeholder. I will still be writing a fix such that %statistic_craft_item%, %statistic_craftitem%, and statistic_craft.item% will all be valid statistics, though for simplicity’s sake I recommend using the default minecraft statistic names, such as craftItem (case is ignored). Of course, specifying item still requires . separation, like this: %statistic_craftitem.minecraft.planks%. I will not be changing the . notation for the specific stat tracking, just the overall stat name such that it is similar to the minecraft internal name.