not a surprise on the hybridizing...and it wouldn't surprise me if they were hybridized by humans before release or on their own....humans as a whole haven't been very good stewards of our planet lately.
One study I read a year or so back said that 95% of the mammals have disappeared. This particular study did roadside counts of roadkill, night time camera counts of critters crossing the roads down there and something else that eludes me right now. But they had been doing this study long term to try to determine the effect the snakes were having on the small mammals and the number of mammals they saw (small stuff like bunnies, armadillos, raccoons, rabbits, bobcats) dropped 95% over the length of the study as the population of the snakes increased.
Gotta love a state that has known for the better part of 20 years that the snakes are a MAJOR problem but they decide they wanna study and see just how big of a major problem and then when they get the results, wait around and twiddle their thumbs before attempting to do anything about it....I know a good number of snakes have been removed by the professional hunters they have hired but I don't know how many and I would bet that it's not even a drop in the bucket numbers wise.