For powerbuilder what is possible is very much dependent on what version of powerbuilder is being used. The most recent versions of Powerbuilder have accessibility interfaces as part of the platform so Accessibility Mode should work for many elements (a google search suggests a Powerbuilder accessibility dll may be required for that to work). For older legacy versions of Powerbuilder it is likely that Surface Automation would be required.
Reliable/robust Surface Automation interfaces can certainly be built if the best practices from the Surface Automation training are followed (I have been using SA for many years without issue) - if you are not sure how to build reliable SA interfaces revisit the training or engage with a consultant with more experience using that interface. It is worth noting that version 6 of Blue Prism has some major SA interface improvements that make it quicker to use and enforces robustness options often skipped such as color tolerence, tiny waits between navigations, waiting for images, etc
