Yes, there aren’t any output transformers in the direct drive amps so technically it is an OTL. However, they put out 5000V. Not sure how many OTLs do that, so the speaker better be up for it.
I run the original Acoustat servos with Acoustat Model 2s with panels modified by Roger Modjeski (I also have Quad ESL with Atma-Sphere M-60s, but converting the Quad to be powered by direct drive). I augment them with a bass array of 4 woofers in a biamp set up. For Roger, the 100 Hz cutoff point is important (his ESLs cut off here), as he wants to avoid male vocals creeping in to the low end, which he has demonstrated to me on select recordings he has. That’s the main reason the LFTs and their 180 Hz cutoff aren’t in my system.