Tis an interesting question.
I've done a bit more digging and it doesn't look as if ammonia will do it. It's used as an anti coagulant in liquid latex, not a solvent.
One quote I found said that acetone doesn't work as his latex gloves survived. What he may not realise is the acetone will go almost straight through into his skin, and hence blood stream. Whoever it was needs to coma and work in our lab where latex gloves were used until H&S said we can't. The acetone made the gloves fall apart quite literally.
Maybe I should have been clearer. The Latex does not re-dissolve, it just breaks down and can be gradually removed, but as I and Pigsty said, the brush isn't much use for anything other than masking fluid application again.
I had the same brush I used for years in my previous modelling spat, just made sure it was cleaned after each use with cellulose thinners.
richc