As with many things, the answer is It Depends (TM).
With the LBs you mentioned, just based on the information you gave, I'd start the 62 OVR Star dev (although I'd be looking at a
lot more stats than just OVR and SPD to make that decision.
That decision would be because LBs are snap-starved to begin with, and LBs are a position that develop based on stat accumulation...the lion's share of defensive plays should be run out of nickel and dime, meaning a lower number of overall snaps for LBs. That player will need as many snaps as I can get them to develop and cash in on the higher dev trait. Also, LBs are a position with relatively minimal on-field impact...lower performance from the position has less impact on the team's performance.
For the O-line, I'd give the opposite answer: I'd start the 69 normal. O-line is a more impactful position, and 9 OVR is a meaningful dropoff (again, depending on a lot more stats than just OVR). O-line is also a position that doesn't get most of its XP from personal stat accumulation....the bulk of their XP comes from team goals and training. So I'd probably look to focus the hidden dev rookie in training, and keep him lower on the depth chart where he can still soak XP without actually having to start.