Hi Steven,
The Find Dangles check does look for end points (dangles) that are near to line features within the tolerance specified. Are you asking to include line features from other feature classes? Because the Find Dangles does consider all line feature classes in the topology. So for example if you have your roads data tiled in multiple feature classes, you could include all of those feature classes in the topology if you copy them all into the same feature dataset.
Regards,
michellej.