from what i've read they can be but its not recomended cause its stressfull but to me its about the same as moving them to another tank i've used that chart on on every cichlid i've bought and it hasn't steered me wrong on the sex of the fish but i'm not much for oscars had several including a pair that i sold cause i didn't want to deal with a bunch of fry after seeing oscars just set in stores for months all you do is look its not like probing a snake
From my experience w/ venting cichlids is that the egg tube usually drops when the fish hits or passes sexual maturity. Some females will lay eggs w/ no male too.
I do believe Oscars will go through a teenager stage throwing fits and acting very strange sometimes. I have had two that went through this stage but it did pass !