Cementing in around soil pipe exiting around brick wall. Is this required?
First of all, did you have any agreements on how the pipe is to be fitted? If paperwork mentions sealing the pipe entry in any way, the final result should match the criteria laid out in the agreement you had with your contractor.

That aside, you said that it is hard to see any gap from the outside of the building so to me, the question on whether or not you need the soil pipe cemented in depends on where the soil pipe is entering/leaving the building.

If the pipe is entering the loft and you are not looking to inhabit the loft, the expanding foam will help with mitigating any water ingress if the expanding foam is protecting the wall cavity from rain water and so I would agree that you don't need to have the pipe cemented in. In fact not being cemented in will make things easier for you or anyone else if the section entering/leaving the building needs removing for repair or replacement. It all depends on how you wish the aesthetics to be.

If the pipe enters/leaves an inhabited space, the interior part may aesthetically be better if it had some cement around it, but that also depends on how the decoration is going to be sorted. If you are plastering the interior around the pipe, you dont need cementing done as the expanding foam used will protect the plasterwork from water ingress.