16,884 votesA commented
I just ran across this thread so don't flame me if this has already been brought up....
Spell check CAN be turned on but its linked to the Android OS, this is not a Microsoft problem. You need to go into the settings and enable it, by default the device keyboard is set to Autocorrect which is the problem. Once you enable/turn on Spell Check you will see the normal red underline in Outlook Mobile for Android in DEX mode. I just turned this on myself so not 100% sure but it seems to work great.
Good luck and post a reply if this works for you.