I don't see the same behavior.
If I make a simple app that just shows activity lifecycles events in a textview, either launched by a launcher intent or a voice trigger, I see:
onCreate
onStart
onResume
when app launches
then if I swipe down or let it time out after ten seconds and then relaunch it by voice command from the ok glass screen, I see
onPause (this happened earlier but I see it now)
onStop (same, happened earlier)
onRestart
onStart
onResume
So onResume is getting called.
So I think the answer to your question is onResume does get called when an app goes to sleep and is called back shortly after. If you are seeing differently my only guess is that it is silently crashing or maybe using so many resources that Glass is killing it. You could learn more by adding some strategic log statements into your code. If it is crashing on pause or on stop then fixing the crash will solve your problem. If you share your activity code I can try to help more.
A more complicated solution to have more control of a long running experience for your user is to set up a live card with a service. The documentation for this here is a little confusing: https://developers.google.com/glass/develop/gdk/live-cards so you could just use the code below as an example.
When you run this live card you will find that the screen does not sleep after ten seconds, and that if you swipe down to sleep and tap glass to awake, you will be brought right back to your live card. Maybe that is an experience you are looking for.
https://github.com/mscheel/GoogleGlass-XE16-LowFrequencyLiveCardBasketballScore