Marketo Landing Page Templates are designed to be easy to use. That being said, you need to come up with a design and code that suits you well in 80-90% of cases. This is best practice for using the system.
In that Template, you can embed tokens or standard SEO that you can later edit on a page by page basis:
http://www.marketingrockstarguides.com/seo-for-marketo-landing-pages-1408/
I highly recommend coming up with a plan to ensure your page is SEOd, even if the marketer forgets to update the meta tags.
It is perfectly acceptable to include Marketo LPs in an SEO campaign. I'd check the Moz Updates to see what the thinking is on subdomains vs. main domains. My understanding is they are sometimes considered separately for ranking. I'd be more concerned with getting your LP to show up for the target kw and that may have to do with how well your main site ranks for that kw.