Does mining multiple nodes with one signhash increase hash power?
no. In order to increase hash power, you need to configure a mining pool. That is why mining pools are so important. I tried to create a mining pool myself, but failed due to lack of knowledge. When a public mining pool comes out, I am willing to participate.
It is equal to the sum of the machine hash power you have. In both cases. So, configuring a mining pool has no effect.
The pool is effective when it takes too long (a month or more?) for each node to mine a block.