I think it probably depends on how well the initial introduction goes and how comfortable your new b is staying in the crate. Ideally, they will hit it off and the new b will love her crate….that said, more than likely it won't be so easy! Try getting your new b over a weekend or at some other time where you will be available to be home for several days. That way everyone has time to adjust...if the new b seems confortable with Diego and the crate you are probably okay leaving the crate in the room with Diego. On the other hand, if it seems like they need a longer period of time to adjust or the new b gets stressed out about the crate it would probably be better to leave the crate in a quite room away from Diego while your gone, at least at first.
Be warned...my b has learned to unlock his crate. We have another b visiting us for a while who I keep in the crate. Today I came home and was greeted by three dogs instead of the usual two. Apparently Manning thought letting his new b friend out of the crate would be great fun. Luckily all three cats have been accounted for and I haven't found anything broken, ripped apart, chewed...Yet! I would get mad if I wasn't so proud of Manning's smarts!
Good luck...I'm sure when you get your new b everything will work out.