Is Barcode Pro compatable with El Capitan?

I can't tell you it is but one of the developers for a bar code app we relied on wanted to charge me $89 to continue to use their software after we purchased it outright and they hid an 18 month trigger in it to shut it down.

My advice to you is search for "web bar code generator" as there are dozens of free alternatives that will write in a litany of code formats for you.

if this is an application that is required for your workflow you should probably check with the developers of that software.