Hi there Clark
You are following the adsense 100k blueprint course and using the pdf supplied - right? If so, I think I understand your question, you are at the section about getting an adsense account and have been directed to come to hubpages and set up an account and write a couple (or more) of good quality, original hubs so that you can apply for your adsense account via hubpages and get it approved quickly.
From this point of view, you can write the hubs about whatever you like, they do not need to be related to the niche, topic or keywords you have chosen for your first wordpress website - the sole purpose of these initial hubs from the course point of view is to gain your adsense account.
However, it makes sense to a) make them as good as you can b) if you have already set up your site and got your main keyword sorted out, to write hubs related to your site so that you can insert a backlink from your hub to your site. You are perfectly correct in what you say about how your site should be set up.
I hope the foregoing answers your question, if not, please drop me a line via the contact me section on my profile and I will do my best to help you.
Great stuff, glad to hear you are already getting 'stuck in'. FYI, I have been following the course for a while and am starting to get some good results - not enough for a full-time income, but definitely the equivalent of a part-time job already!