Web Server Monitors

You can find this information in the LTM-DNS Operations Guide on page 18 and 19:

HTTP receive strings are matched against both HTTP content (for example, HTML, JSON, or plain text) and the HTTP headers.

So, yes page content can be test.

See: https://support.f5.com/content/kb/en-us/products/big-ip_ltm/manuals/product/f5-ltm-dns-operations-guide/_jcr_content/pdfAttach/download_0/file.res/f5-ltmdns-operations-guide.pdf