I think Escape didn't want any security stuff or things to get in the way, just a plain normal battle with Sidious against HK, and took the death star just for it's looks. And I don't think his intentions to this battle was if HK could blow up the Death Star or not. Am I right?
Anyway, I don't see how HK is going to avoid Sidious force lightning, it will probably destroy him right away and we havent seen anyone dodge it really. He could do it with one hand and deflect with the other. He could also pull in his guns.
Although HK is the best assassin droid ever I don't think he stands a chance to the power of the Emperor.
Or did I miss something special that HK could do against him?