I've never had any trouble with any fully submersible heater touching silk plants or even substrate a little, even the ones that don't have rubbery ends. Nothings burned and no ones died. xD I don't think the surface really gets all that hot, like aokashi said....if they did it probably wouldn't be safe for fish!
I would be careful with that specific heater model though. I got one when setting up one of my 5.5 gallons and once I had everything set up and going and added the fish, I noticed after a few hours my boys were acting a little strange...and no just a new-tank sort of strange. I had a really bad feeling. The water also smelled a little funky....like bad not-fishy funky. I got my boys into clean water and broke down the whole tank, rinsed everything VERY thoroughly AGAIN....and that rubbery end of the heater popped off very easily and under it was an absolutely AWFUL smelling glue substance. I trashed the heater, got an Aqueon Pro, rinsed everything AGAIN, set it all back up, added my boys, and everything went smoothly after that. I'm convinced to this day that that heater was leeching something into my tank, and I'm very glad I trusted my instincts and acted quickly before I lost my boys.
So just be careful......I might have just gotten a bad one, but I'm rather skeptical about the Top Fin heaters now...