Sorry, meant to respond to this a few days ago.
I certainly wouldn't say it's inherently challenging, but it depends on what you're using as your site search engine. If the engine is only capable of indexing local assets (stored in a CMS database) then it isn't going to be able extend to remote content that is only accessible via HTTP URL.
What you can definitely do easily is use Google Custom Search to index your LPs. Out-of-the-box, Google'll give you a Search box that is limited to results from this index, but that's probably not what you want, because it'll mean you have two different search areas. Instead, your developer can fetch results from Google under the hood using their XML API, then integrate those results with the on-site results before displaying them all.
To add to what Sanford says above, you may choose to create a custom domain alias (CNAME) to further identify and be able to create an XML sitemap that you can present to your custom search for your site.
This can help to be a specific identifier beyond many of the standard domains people setup like e.mydomain.com and such.