How risky is it to drain window wells into an interior drain tile system?
You're right on target with the questions you've asked.  You want to prevent water from collecting around the house.  Ideally, it's best to avoid water being there in the first place.  If you can't do that, that next best solution is to give it a place to go to get rid of it as quickly as possible.  That can be accomplished on the exterior or the interior.  If you put in a system to get rid of water, the benefit will come from letting it get rid of as much problem water as you can get into it.  

To drain the window wells, don't just drill holes and let the water run down the wall into the floor drain.  Stick a pipe through the wall with the wall opening sealed around the pipe, and direct the water into the drain while keeping it contained.  Use some form of screen or filter on the inlet so the pipe doesn't get clogged with debris.

As you noted, once the basement is no longer sealed, water can migrate in as well as drain out.  The interior drain, itself, is a potential path, and any other exterior water you provide with a path adds to it.  It is critical to have a reliable and redundant system to get rid of the water or your basement can become the collection system.  

Sump pumps don't last forever, so have a second, backup pump.  Power can go out in a storm, which is the likely time when water will be feeding the system.  So use some form of battery backup or make one of the pumps battery- or dual-powered and include a provision for keeping the battery charged and tested.  Or have the pumps on a backup generator.