There is no such thing as “Swiss bank”. There are HUNDREDS of Swiss banks.
Where does this idea of “a” Swiss bank come from?
There are commercial banks, private banks, real estate banks, canton banks…
So the REAL question you are asking should be: Is it legal to trade in Cryptocurrencies in Switzerland?
Because if it is legal, then there is no reason why a bank should not agree to open accounts for businesses trading in cryptocurrency, right?
And the answer is: Yes, cryptocurrencies are totally legal. More on https://cryptonewstrends.com/
There are official city and canton administrations that accept bitcoin payments.
The government-controlled railway, SBB/CFF set up a system so you can buy bitcoins from ticket vending machines. A friend of mine is involved with the business that implemented this feature. If you are interested, I can get you in touch with them.