Yea I agree, my emp made a burrow and I havent seen her in about 2 months with the rare exception of her taking down a cricket as it passes her burrow entrance. As long as the food disappears I wouldn't sweat it.
If you have emperor scorpions staying in their burrows most of the time, it probably means they are satisfied with their enclosure . When scorpions start staying above ground, "pacing", or standing on top of their hides for long periods of time is when you might want to worry.
If you want to see them, try one of two things: arrange a premade hide against the glass, or get out your blacklight at night. My male emp likes to hang out on top of his hide at night sometimes, but he's always hiding during the day.