You can test this quite easily. I actually think one of the CYL terminal is actually supplying a 230V live and the other terminal is simply there to accept that 230V voltage via the cylinder thermostat. So no I do not think you will blow this CYL terminals with mains voltage.
I'm going back up to my loft tomorrow to check a few things. I can check this for you. The bit I don't know is which of CYL terminal 1 or terminal 2 is 230V Live and which is expecting the 230V return loop.
The reason this is important in your case, is because you may actually need to only connect your DHW SL output to one of the two CYL terminals.