After road testing my OM-1 out in several instances when I first took delivery, it's sat in exclusively ES. I see no reason not to. It's essentially NO wear and tear on the camera which is a plus. I've not seen any rolling shutter no matter what moving subjects I've shot. Certainly, superior to the previous camera I had, a Canon R5 in this regard. I didn't even note there was an "Auto" mode. Wonder what shutter speed it switches over to ES from MS? The other cameras I've used don't have that luxury.
Are you thinking of anti-shock mode (diamond symbol)? It rolls from electronic first curtain to full mechanical (both curtains) at 1/320. Silent (heart symbol) doesn't do this, being full electronic at all speeds.
Confess I don't fully understand how speeds are handled above 1/320 in silent mode, because it's emulating that higher speed.
Cheers,
Rick