Trying to sue Kemper for their amplifier is like trying to sue Sony for the tape recorders they sell, or the CD/DVD writers. In that regard, I think that the reason why companies have threatened legal action is use of their brand name and products to sell something.
That is something they feel could hurt their business. If they admit that the Kemper can cop their amps, do you know how the market would react? All those tube guys who say a digital device can't cut it? The Axe FX brigade?
I'l just warn all those people here: don't do it, or it'll come back to haunt you.