It is supported to add instance of CQWP into Page Layout.
Possible reasons why CQWP results are not visible:
- Javascript/CSS that affect the visibility of web part
- Verify source settings for web part. In case if page and page layouts located on different sites and the source property is configured to
Show items from the following list
orShow items from the following site and all subsites
then this could be the reason. In both cases for for source property the relative path could be specified.