I don't have definitive information here. But a google search reveals that Kindle has improved their support for soft-hyphens recently. But mostly this is done within the reading system.
While Amazon, intent on keeping developers miserable, declined to explain how their new hyphenation engine works, it actually appears to just be support for the Unicode soft hyphen character (U+00AD). If Kindle encounters a soft hyphen near a line break, it considers it a hyphenation opportunity.
I did a quick check of Google Play Books and Kindle for Android and see that body hyphenation doesn't seem to be turned on. I seem to remember that iBooks hyphenated body text (maybe). The Amazon formatting guidelines doesn't mention anything about it.
I suspect that unless you are using specialized or technical texts with a lot of long multi-syllable words, it doesn't make sense for the author/publisher to add the soft-hyphen character yourself.