Siebel comes in many shapes and sizes - it can be browser based, it can be a locally installed windows application, and it can be massively modified and bespoked by each organisation to look and behave differently.
If it is a browser application you wish to interface with, than you should be fine, my one bit of advice would be to ensure that each robot user is set up in the same way, from memory Siebel can have a lot of user specific settings.
If it is the local install you are using than our Windows/Accessibility/Surface Automation interfaces should give you everything you need to be able to interact with screens.
You could also reach out to your Blue Prism mentor/DEM in relation to potentially using a Siebel API object that has been used at previous Blue Prism clients for Siebel versions 6 onwards.