Impacts/dependencies feature started and will be shipped in 9.5: https://github.com/glpi-project/glpi/pull/5954

Feature will be shipped for 9.5

Work in progress : 

https://github.com/glpi-project/glpi/pull/5892

work for impacts/dependencies graphs is in progress: see https://github.com/glpi-project/glpi/pull/5954

done in https://github.com/glpi-project/glpi/pull/6008

There are already community integration projects between GLPI and Zabbix.

https://www.zabbix.com/integrations/glpi

Done in GLPI 9.4 : https://github.com/glpi-project/glpi/pull/4482