This what I claim to be true. I have not taken an OM-D apart, though. I have only seen quite a few images.
Some time ago there was a "mistake" at Olympus France web site. They said in a spec line that Olympus PEN E-PL5 has no low pass or anti-aliasing filter. This spec line was removed and it was said that all Olympus bodies with Sony 16MP sensor are alike.
Before this incident I had not thought about LP filter in OM-D. I had noticed that it must be very thin because there is some aliasing and moiré time to time but nothing to be worried about. Also OM-D images are very sharp which also made me think that LP filter must be very thin.
I have used digital backs which have no LP filter since 1997. I went through my old images and checked the frequecies where aliasing and moiré can be seen and compared to them to OM-D images. One of my reasons to play with Nikon D800E was to check its files in Lightroom. While it is said that D800E has no low pass filter, techically it has some kind of a filter and it works a bit differently. So, I loaned a couple more new digital camera bodies which have no LP filter.
This image is an enlarged crop from an OM-D frame showing moiré patterns.
My conclusion is now: Olympus OM-D has no low pass filter at all.
Is it a good or bad thing then? No. It just is what it is. I was curious.
Moiré and aliasing are not problems in RAW files, and when moiré is present it is easy to be corrected with Lightroom tools. Only every now and then there is a jagged edge which needs some hand work. With JPEGs I have not seen any complaints at photography forums.
So this is sort of a non-issue, but I thought to let you know... ;-)