I think it will all be removed if you clean your equipment properly.
Other point is that most of the "Dry Enzymes" aren't the same as A&B Amylase in barley malt. Many are cropped from bacteria, some will survive up to 90oC, they will certainly work at much lower pH than will the typical barley enzymes.
Amylase is a catch all term for any enzyme that will degrade starch into sugar, the stuff in your spit is different to barley amylase to. People talk about Alpha and Beta Amylase, barley also contains Gama Amylase, its there, it just doesn't get a play as its active at a pH of about 3. More complicated than you might expect.
I have used Dry Enzyme in the mash, it does the same thing (reduces starch to sugar) but at least its fully denatured in the kettle and doesn't tend to run on until the beer is too dry, gives most of the benefits without any of the potential drawbacks of adding to the fermenter. There are commercial Enzyme preparations made specifically for adding to the mash, but I have found a packet of "Dry" does the job.
Mark