No belt can meet the EN standard for a harness (for obvious reasons).
Arguably a climbing harness (one of the tougher-wearing ones) is a _better_ choice for lifelining than an SRT harness (higher point of attachment, so reduced risk of inversion).
Using belts (or just free-climbing) a ladder and on traverses is still de-rigueur in the Mendips and (to some degree) in South Wales AFAICT. Typical Mendips rig on Swildons when I got there yesterday (ladder on one bolt, lifeline on the other through two chained ancient steel carabiners and, for reasons which still elude me, a pulley). I rigged my own lifeline on a sling from both anchors (which is admittedly not necessarily helpful; probably I should have de-rigged their set up entirely but Swildon's rigging practice is a bit of a nightmare). Unfortunately the pair whose ladder it was overtook us just before we got there, and in a (genuine) attempt to be helpful free-climbed the ladder to try and bring us up quickly but I wasn't quite ready, and then some rope confusion happened where they pulled up our rope etc... then free-climbed back down the ladder, and I had to ask (hopefully not too impolitely) not to do an over-the-shoulders belay (given that my belayer already had the rope in an Italian hitch)... if you are reading this, thanks for trying to be helpful and sorry we weren't very easily helped! I also wanted to rig our ladder onto the stubby stal to get it further away from the water (one day perhaps cave conservation and common sense will prevail and that pitch will get a fixed ladder, but I suspect it will still be a while...).
I was using a single sling for an improvised harness including leg loops (I don't actually own a 'caving' belt, mine is a Black Diamond trouser belt).