Steps to reproduce:

1. Register Host in Zabbix
2. Add "Linux by Zabbix agent active" template to the host.
3. Try to add any "DELL PowerEdge R*** by SNMP" template to host
4.  

Result:

See error message about conflicting discovery rule "net.if.discovery" (type - HTTP agent) which is present in the Linux template as well as the DELL poweredge template.

Expected:
Ability to add both hardware (DELL Poweredge) as well as software (Linux) monitoring templates to the same host.

NOTE: I worked around by renaming the DELL Poweredge discovery rule from "net.if.discovery" to "netif.discovery"