Well, if Rangers is a "go," you may be right.
However, in the unfortunate event that Rangers is not picked up, it would be nice to see these familiar faces. First of all, not everyone watching Jeremiah will have also seen B5LR. Second, since actors always need work, I think JMS will share the wealth with people he's done well with in the past.
As to "overusing," well... with an original concept from the ST: TOS episode Miri, characters and plot points from Mad Max: Beyond Thunder Dome, and the underground base motif from Jeremiah's Showtime stablemate, Star Gate: SG-1, -- how much of an issue can "overusing" be?