Of course you can do DoS and DDoS against hidden services. The easiest way to prevent anyone from reaching a hidden service is to enumerate all of its introduction points and spam them with fake extend cells to exhaust their processing capabilities. You can also DDoS the hidden service in a traditional way, you simply need the nodes on the botnet to send their traffic through the Tor network up to the hidden service. It is just a normal server, it is not immune from anything. The server software itself could also have some bug or configuration issue that lets an attacker do non-bandwidth resource exhaustion. Tracing hidden services to entry guards is possible as well, at which point the entry guards can be DDoSed and if the HS is set to use strict entry guards then it will go down as well. In summary, you clearly have no idea what the fuck you are talking about so please stfu and gtfo.