You could always try growing corn yourself if you have some room and a suitable environment, then you'll know if its safe for consumption.
The main concerns I'd have with commercial corn leaves (assuming the leaves/stalk etc) is safe for piggies in an of itself is as mentioned pesticides. Most pesticides are targeted in nature, that is they're effective against specific groups (generally most pesticides are insecticides- mostly effective against insects). And as mentioned some pesticides simply cannot be washed off since they're not ON the plant but rather IN it. These are systemic pesticides, they're applied to the plant/soil/seeds and the plants absorb the chemicals, incorporating them into their greenery and other portions. You cannot wash them out anymore than you can wash the green chlorophyl out.
However, these systemic pesticides generally do not cause issue to humans and as they describe it "non-pest species" due to their method of action (such as requiring specific proteins in the target species to bind to that humans lack) however, I do not know what they describe as a "pest species" with respect to these pesticides. If your animal is fine eating the silk and husks, the leaves are probably fine though, with respect to systemics (since they'd also be in the husk/silk- albeit at a lower concentration since they're younger structures and will not have had as long to absorb the chemicals). The main thing to remember is that GPs aren't humans, so they may react to pesticides that don't affect humans.
Some commercial corn plants also utilize Bt toxin GMOs. Bt toxin is targeted to insects, not humans or other mammals (such as GPs). However, its expression is more likely to be concentrated in the leaves and non-human consumed portion of the plant. GPs may have a reaction to the protein itself, rather than any toxicity effects.
There have been studies showing immune response in mice, however the validity of most of these studies I find to be questionable since the test groups are usually something like 1)organic corn 2)pesticide corn 3)Bt w/pesticide and the negative effects are usually of a comparable level to the pesticide group, which may imply the issue is from the pesticides, not the Bt, and with the test groups it is impossible to say Bt is the cause since its not being tested by itself. However, most anti-gmo publishers will hide that aspect of the study in their reports and simply call it the "Bt group" and focus on the difference between the organic and bt w/pesticide group, which as mentioned may be the fault of the pesticides rather than Bt.
But anyway, TL;DR the leaves of commercial plants may be more highly ridden with pesticides than the husk/silk portion of the plant, and you may be unable to remove them with cleaning. The pesticides may or may not effect GPs but because the leaves will likely have more of the compounds there may be a higher risk of reaction, even if more of an allergic reaction.