Example 1
A: We don't need some employees at this company.
B: mm/hm/um huh/okay.
Does this only mean that B is paying attention, like saying "Okay, I am listening"?
Example 2
A: We don't need some employees at this company.
B: I agree/Yes/right.
Does this mean that B is also thinking that they don't need some employees at the company?
B isn't saying enough for someone reading the transcript to know exactly what they were thinking.
Generally "Yes", or "I agree" do mean that B's opinion is the same as A's (but watch out for "I agree but..." or "Yes, and ..." which might be tactful ways of disagreeing!) And sounds like "hmm" indicate thought, but not agreement. "Okay" could mean almost anything.
To understand what B is really thinking, we will have to wait to hear what they say next, or even better find out what they do. (Remember B can say "Yes" while thinking "No".)