Steps to reproduce:
1. Create a template with host dashboard
2. Create a host and apply hostgroup, apply the template created on step 1.
3. Create Zabbix Admin type user, grant permissions (read or read-write) on host created on step 2.
4. Try to view the host dashboard from user created on step 3.

Result:

Expected:
Able to see the host dashboard.

If I apply the same hostgroup, which I grant permissions to, to the Template created on step 1. , then the Host Dashboards work as expected.

Tested on 6.0.19 and 6.4.4 (Used template groups instead, same issue)