Summary says it. I also had to merge app-text/dvipng since it is not shipped with app-text/tetex.
I dont see any requirement for app-text/dvipng in the pidgin-latex code... its in the tree as a copy of the 1.0 ebuild
Without dvipng the latex code, i.e. '$$ a(x) = b * x $$', is not transformed into a picture to represent the code in the chat window.
the code uses three commands: latex, dvips and convert