My planted tank in which I had my 7" WC Rotkeil, 2 Bolivian Rams, 1 Keyhole, 2 P. taeniatus Dehane, a couple of hatchet fish, 4 lamp eye tetra's, 4 dwarf loaches, 2 Sumatran gobies, 1 GN pleco, 1 Adonis pleco and about 12 mountain minnows (severum snacks).
Initially my Sev would very occasionally attack my plants - but very rarely and on the occasions where he did I used one particular algae scraper to ward him off. I did this for months and he learnt not to do it, they are intelligent fish and can be trained certain things.
But then
I wanted to try a tank without plants, so
I pulled them all up, lol. So much for him doing it.
He's only eaten all of my Amano shrimp (to be expected anyway) and a few Lamp eye Panchax, but he hasn't touched the dozens of mountain minnows I put in there JUST for him to eat. Oh and I had the pictured set up with the Sev in it for a good 6-7 months at least, so it wasn't just a short term thing. It can be done but it does depend on the Severum and you can influence them to an extent, again depending on the particular characteristics and intelligence of that fish.
On the whole though, Sevs are notorious plant shredders and very effective predators.
Dithers that have worked well for me - White tip tetra's, Rummy nose tetra's, Red eye tetra's, Black phantoms (although I have lost a couple as they can be stubborn), mountain minnows (annoyingly and surprisingly) and hatchet fish.
Blair.