I use the self-timer a lot on all of my cameras when I am trying to maximize sharpness, so I frequently recommend that to others.
For your situation, I do have a concern though. The self timer release for the OM-1 isn't particularly accessible. In a true macro environment, where distances are small, I think it is quite easy to bump or jar the camera when reaching for that release. That may not cause a problem with image sharpness due to shake, but it can play havoc with plane of focus and composition concerns, especially if you are using mirror lock-up.
For that reason I think I would prefer mirror lock-up plus good cable release or air bulb release.
Your experience with the self-timer release may be better than mine, especially if you are not left-handed (I am).
EDIT: I see that Q.G. and I are mostly in agreement. With respect to mirror lock-up, I find that I have more success operating it without causing the camera to move than I do with the self-timer.
Paradoxically, this is one of the reasons that the amateur oriented OM-G (OM-20) may be advantageous when compared to the OM-1 for some things. On that camera, the self-timer function stays engaged between shots, is activated using the normal shutter release, and causes the mirror to lock up (pre-release) at the beginning of the timer process.