Ok, to be fair I'm not a physicist but it would seem to me that if you get a stream of mixed particles and anti-particles, they would annihilate, thus not producing a mass difference.
Quick thought experiment: two particle-antiparticle pairs get created:
p1-ap1, p2-ap2
In regular space, after a very short amount of time p1 annihilates with ap1 and p2 with ap2. Net result is zero additional matter and energy, otherwise we'd just be creating random matter and/or energy everywhere.
If the same happens at the event horizon of a black hole and let's assume purely by chance, p1 and ap2 fall in and p2 and ap1 do not. After a short while, p1 and ap2 annihilate inside and p2 and ap1 outside. The result should be effectively the same as in the previous case, thus zero net energy and/or matter on either side. Thus, also no radiation and mass loss.
It'd be nice if an actual physicist chimed in at this point and told me where I went wrong :)
For the charge to matter, you're saying that charges infer positive or negative mass. But that's original responder's point.... both the particle and anti-particle both have positive mass regardless of their charge, which is a different attribute.
Consider how it is you are conserving energy/mass in your thought experiment. Seems like you might be creating a back door whereby that mass/energy is not conserved in order to preserve charge conservation.
The actual physicist is Richard Feynman, and here is a Feynman diagram of a particle-antiparticle annihilation.
* https://commons.wikimedia.org/wiki/File:Mutual_Annihilation_...