Yes and no,
Benefits Green Silver Gold Diamond
Advance seat reservation1 & 2 - Yes Yes Yes

1 Members' spouses can also enjoy this benefit when travelling with the member.
2 Subject to availability at time of reservation and is only available on Cathay Pacific marketed and operated flights and not for joint venture or codeshare flights.

But when I purchased a ticket online (direct with CX) for my mother few months ago, I managed to find a exit row for her (out of luck) and she wasn't bumped off to non-exit row seats when checked in.