no, and no.
there are workarounds:
"indicator that tells whether the clip has been used in the timeline yet."
if you select your timeline clips, and COLOUR them,
(option apple 2-6 colour the clips, option apple 1 is no-colour)
the browser clip will be coloured too.
"is there a "locate clip in the timeline" feature?"
if you open the clip into the viewer, and park within the in-out points,
then match frame (f) will take you to that particular frame in the timeline.
you can see the issue here, no doubt: you need to be parked on a frame that has actually been used in the cut, otherwise if wont work.
cheers,
nick