amcas had no problem with my stats class under the psych dept as i stated before. if your classifications are legit, i really doubt it will slow down your application too much. they might become suspicious if you have a whole bunch of strange classifications. i only had the one, and at my liberal arts college stats was only in the psych or econ dept. if you go to a school with a stats dept or math dept that offers stats and you didn't take that one, you might have more trouble. or if your stats class has a strange title and is not in the math dept, you might have trouble.
a couple of my grad school classifications were changed by amcas, but it was no big deal.
i really think oceanography is pushing it. geology courses are not supposed to be bcpm --- amcas even says oceanography should be classified as natural/physical sciences. it may be a little arbitrary that it's not bcpm, just as engineering courses are not, but that's the way amcas wants it. statistics is supposed to be classified bcpm.
you may as well try to classify the teaching assistant position. i'm sure amcas has a rule for whether or not it should be bcpm. if they don't like it, they'll change it for you.