Does hiding a tool stop other people on my account seeing it?
No. The arrangement is yours alone. Everybody else on the account keeps their own, and hiding changes nothing about what anyone is allowed to do.
From the guide Arranging Your Tools & Sections.
Hiding is not a permission
Hiding an entry removes it from that list and does nothing else. The page still exists, search still finds it, a link still opens it, and anybody else on the account is unaffected. If you need to actually stop someone reaching something, that is a role and permission question, not a layout one — see Roles & Accounts.
Read the whole guide: Arranging Your Tools & Sections