How do search committees use feedback from one-on-one faculty meetings during an academic interview?
I am in a US R1 institution in a department of computer science.

All departments have their own style. Ours is something like this:


Each candidate is "governed" by a search committee (we often have multiple searches in different areas) consisting of 4-5 faculty.
Each candidate is "hosted" by one specific person on the committee: the host's job is to be the candidate liaison to the process, as well as managing the interview schedule, and making everything run smoothly from the department's point of view
Immediately after the interview, the host sends out mail to the faculty requesting formal feedback via email. The host will also typically buttonhole people in the hallway to get informal "vibes" as well. 
after the formal feedback is collected (and anonymized depending on how things go), and after all candidates have been interviewed, the search committee sits down to assess the pool.


At this stage, faculty feedback plays the following role (the committee has already discussed the technical merits and strengths/weaknesses of the candidates):


  
  Is there a clear consensus in favor of a candidate ? 
  Are there candidates that are drawing strong (and well-founded) opposition from the faculty ? 
  If the committee decides to choose one particular candidate to put forward to the faculty at large, will there be significant opposition,
  and why ? 
  what is the overall sense that the faculty appears to have about the candidates in general ?
  


After this is done, the committee might choose to:


present a candidate as a consensus choice
present two candidates as co-consensus choices that the faculty at large can vote on
decide that no candidate has crossed the bar for a faculty-wide vote.


To answer your specific questions that aren't covered above:


no one person (not even the chair!) has a veto over hiring someone, but obviously people closer technically to the candidate will have a "weightier" opinion. The way our structure works, it's possible (though unlikely to happen) that the committee will nix someone that the faculty all like, which is a sort of collective veto
faculty are assembled to meet the candidate based primarily on possible match of interest, and occasionally also for tactical reasons :). The host will make sure that people who are stakeholders in the hire meet as many candidates as possible. But there's of course an element of "who's available that day".