The lizard carries parasites that can and may get spread to the frog, being as they're insectivorious. The most commonly found pet trade lizards, as well as cheapest, are Anoles, Iguana's, and Savannah Monitors....none of these are bred with any regularity in captivity to supply the demand for them, so majority are CH or WC, therefor they carry the possibility to spread those various parasites to the frog. Not worth it, plain and simple...
Unfortunately, some people do not care about spreading parasites.
Originally Posted by AndrewH
Show reliable sources including breeders, and lab work done showing the benefits of rodents in the amphibian diet
That would be nice, however some people prefer to talk a lot but never show proof to back up their words.