Your blog should match your website style - at least, in most cases. In the case of THIS blog, I'm using the built in blog software that came with the Concrete 5 Template that I used to put this website together. However, this is an example blog, in another part of the interwebs, I have another more personal blog, which uses an entirely different look and feel, in fact, it's done in Blogger, which is now a Google property. You can find it here and see for yourself that it has really nothing to do with this website at all.. it's just my detached ramblings about things that I observe - certainly not appropriate to put on a professional site that purports to sell my business to you. But that's okay, because I can and will put references to this website there too.
Some Features of using a separate blog
Some blog sites, such as Wordpress can comprise an entire alternate site, with their own separate audience and their own SEO, or Search Engine Optimization - the technique that gives you better placement in searches in Bing, or Google, or Yahoo. Take it from me, and everyone else on the internet, Wordpress is HUGE.
This blog for instance will probably never be 'cited' or come up as a separate blog, simply because it's just another component of my sales site. But that's just fine - I don't want it to! That's because only while you are on this site, is this blog relevant. So you might want to make that decision, of should your blog be just inside your site, or should it be more widely distributed, as it were, and include topics that are not part of your main business.
Gallery pages are the same way
I have decided to use a separate Gallery software to display my photography. It's called ZenPhoto, and again, it has a completely different look and feel than the one on this site - that's because many of the pictures would be off topic for this site's purpose, but I love sharing my pictures, and love to cite them on say, Facebook, or Google+, or in Twitter. While there is some overlap, the other determining factor is ease of use. The ZenPhoto software is MUCH easier to update than the gallery on this Concrete5 website.
I also use Flickr.com a lot because - let's put it this way; would you rather have a shop out in some lonely field (the vast expanse of the internet) or in an art gallery, where other people are doing pretty much the same thing, and going to nearby places and getting all the benefits of location, promotion, and customer base? I would hope so.