yes everyone can use it to an extent. However, Felix always suppresses his mana signature when not in combat and only uses what he needs to for spells, never putting out more than the bare minimum of what the current task requires. So most of the time Felix is invisible to manalysis. Though with that said, if Yuno was particularly proficient in manalysis and was paying attention she could in theory have sensed the manaegis boots Felix was using to scale the trees.