Is It Safe to Reuse the Same Salt in Bcrypt Password Hash (Specifically for Chaining Hashes)
I am not aware of any research for this problem and it is difficult to declare anything as safe without a good reason. 
Probably that's why everyone holds back with answers.

Suppose, however, the main attack against these BCrypt hashes is a dictionary attack, probably with custom hardware,
I can't see a weakness in any of the solutions. Reusing the salt for different passwords weakens a scheme. That is not the case here.
For other attacks (cache-timing...) this shouldn't matter. 

But you sail in unknown waters.