No they aren't but, put Dexron in a Ford transmission that requires type F and see what happens.
Don't keep us in suspense.
They become a slush box. It's been my experience after 45 years in this business that in some cases choosing the wrong fluid for your transmission can indeed destroy it. Many fluids don't mix well and quite frankly since the OP is discussing a stock transmission where all the fluid can not be removed the only safe answer here is to replace the fluid with approved fluid. Now if you are building a high performance transmission with all new frictions and a converter where all the fluid is going to be replaced then starting out with type F is OK, but just replacing half the fluid with type F isn't the best advice in my opinion.
Here is some reading and a Ford transmission fluid history lesson.
