Can a BJT base-collector junction be safely used as a diode?
(1) Yes, it will work. 

(2) If I recall correctly \$V_{CES}\$ (B version) will have \$V_{CES} &gt; V_{CEO}\$. 

(3) \$V_{CB0} &gt; V_{CES}\$. 

(4) Forward voltage will be around \$0.7V\$.

(5) \$I_{Cmax}\$ 

(6) Hard to say because keep in mind that the BJT was not designed and optimized to be working as a diode. So, you should use an ordinary diode in your application instead of BJT's. Because you do not get any benefices from using the BJT. 

And if you want low forward voltage drop bought yourself a Schottky diode.