Yes, they can (and sometimes do) hatch indoors, such as when they are not noticed attached to someone's fresh-cut Christmas tree and that tree spends a long time indoors; the warmth advances the development of the mantis eggs and they hatch early.

While it can be a useful educational tool for teaching children about insects, for example, we would not recommend encouraging this otherwise. Not only if the species of mantis is non-native, as most in our region are, but also because they will be difficult to feed properly. (That said, mantids often can cannibalize each other if kept in the same container. They are fairly indiscriminate in what they eat, as long as they can catch it.) Some people raising mantids feed the hatchlings wingless fruit flies and later "pinhead" crickets, both of which can be obtained from specialty pest stores that cater to feeding poison dart frogs and similar small insect-eating pets. As the mantids mature, they progress to larger prey.

Even if released outside, the invasive mantid species are so comparatively ubiquitous in Maryland that they probably won't have too much detriment on the ecosystem since they are already widely established. In principle, though, invasive species of any type (plant, animal, etc.) should not be released intentionally.

Miri