It seems to be not possible to use two different items sources in a trigger expression with a template, however it works fine on the host level.

When I'm trying to use expression such as

{Template Product:inactive_nodes.str(Inactive)}=1&{Template OS Linux:system.hostname.regexp(myregex)}#1

The error after saving it is

Trigger "Inactive nodes found" belongs to templates with different linkages.

It should be possible to use these two different items sources on a template just as it is working on the host level now.