If an adwords landing page and all pages linked from it are in accordance with all advertising policies, but there are another pages(SEO version) on the domain, which might not be in accordance with adwords policies (but are not reachable from the landing page) could this affect the approval of the ad with the landing page or my adwords account?
In other words, if my adwords landing page is www.domain.com/landing_page.html , should I make sure that also www.domain.com and www.domain.com/anypage.html are in compliance with adwords advertising policies even if there's no link from www.domain.com/landing_page.html to them?
You'll be OK. As long as your Adwords landing page is in compliance, that's pretty much all they check. They have no reason (or resources) to check all other linked pages. What matters most is the landing page itself. Plus, you've separated the two. They're not going to check every page they are aware of to ensure you comply with Adwords.