I only have bta's. I have around 25 to 30. Out of those around five have stung corals. When I noticed coral getting stung I relocated the Nem or coral. Which ever is easier. Currently I have nems on top of zoas. Zoas are doing just fine. I also have a stinger on a few magician palys and they are not doing fine. I left the Nem there though because I have 100+ magicians. Don't mind losing a mini colony.
My main stingdrs are my gonzo sunburst and rose. My least aggressive are my rainbows. They have been on or near a large variety of coral.
To answer your question I don't mind the rainbows touching blasto. I would not leave the blasto near the rose or gonzo. Yes nems touching have been fine because only my nems that touch everything have been in contact with them.