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It is possible to combine ASPX page templates and portal engine page templates on the same website.
If you have a website built using the portal engine development model, the master page and all other pages use portal engine page templates. Unfortunately, you cannot "insert" ASPX pages directly into the portal engine master page.
However, you can use the following workaround:
Create a copy of your portal engine master template as an ASPX master page (.master file) and assign it to your ASPX templates.
Take all content (HTML and controls) that you have above the Page placeholder web part on the portal master page and place it into a new user control named Header.ascx.
Take all content from below the Page placeholder and place it into a user control named Footer.ascx.
Delete the content of your portal engine master page and replace it with the following web parts:
Remove the content from your ASPX master page and replace it with the following controls:
You can now manage the header and footer in a single place for both the portal engine and ASPX master page.
Note: When you create a website with both ASPX template and portal engine pages, you cannot use page nesting between the two different types of pages.