Custodial LN is like leaving your bitcoin on an exchange. If someone is selling on darknet markets AND using custodial LN then they kinda have a death wish.

Onchain fees are 2-3 sats/vb at the moment. Anyone can open a self custodial channel and turn on MPP so that small denominations are getting routed around. 

I think it would be naive to think they didn't have LN nodes up and running, but like I said,  they're a black box. They make sh$t up like with the bitcoin fog guy and get away with it. Who knows what they really can or can't derive from the LN network.