I use water soluble fertilizer applied with a hose-end applicator all the time, Steve. My stags get sprayed along with all my other 1000 tropical plants. So the short answer, at least in my experience, is that the foliar fertilizer is perfectly OK.
Yes, young stags do best when kept constantly moist (not soggy wet though) and they do grow pretty rapidly. I generally have to water my mounted stags every single day, spring and summer, at least those young ones. When the stag gets large and has multiple basal fronds forming a thick layer of "spongy" material, watering will be much less.
