From my own experience I would say so. Technically platforms like Instapage, which I have extensively used, do have an SEO feature built into them, although I really don't think they work - is very basic and any good SEO person would know that meta tags and key words are only the tip of the search iceburg.
Landing pages should always be a/b optimized, if you can pull that off yourself without these platforms then go ahead because ultimately you can customize to full seo needs.

I actually think they create more problems for SEO rather than help. Because I have numerous elements being tested, generally the content is similar, and this creates duplicate content issues. Typically I use ROBOTs tags to hide my landing pages from search engines and prevent dupe content issues.

That being said, whatever it is you learn from your landing pages should be used on your website pages that ARE seen by search engines. Use them to improve your content and offers. This will improve your site performance overall and help your website SEO because of good metrics.

Having experience integrating Unbounce these are served on a third party host and are therefore not indexed as part of your domain as they are blocked. I would be very wary of using these if you are considering creating a landing page that is very similar to the theme of another existing landing page within your main web page navigation.

As others have mentioned you may want to look at controlling how these are crawled, blocked or viewed by search engines if you are considering using these as part of any future strategy.