Yes... but why?

If a character appears for only five episodes of a full season or so, wouldn't it be sufficient to handle the respective actor as a guest star? What's the reasoning or advantage?
The advantage is your actor doesn't go looking for other work, because a television contract gives the show first call on an actor, meaning he/she must be available for the show. If you have a guest star individually negotiating, then they're allowed to go work on a movie or whatever else instead and they're not guaranteed for the episodes you need them for. That's why Draal ended up not being in War Without End.
Granted, Babylon 5 always had the strange habit of including actors in the main cast, which would have been guest stars on most other shows. For example, Aron Eisenberg appears in 12 out of 26 episodes (= 46%, compared to Tracy Scoggins' 23% in Crusade) of DS9's 7th season, yet he was not part of the show's main cast.
Since Joe planned a lot of Babylon 5 episodes in advance, he knew roughly where each recurring character was needed and could give them a contract for only a certain number of episodes. That way, the production wouldn't pay an actor for all 22 episodes when they only appear in 13, but the actor would also be guaranteed to be in the 13 required episodes without having to renegotiate for each appearance.
The weirdest thing was Season 2 in which guest star Jeff Conaway appeared in as many episodes as main cast members Robert Rusler and Mary Kay Adams combined.
Jeff didn't have a contract in season two, but he wanted to keep doing the show and was written into about eight episodes.