first of all, You are right, Fiori is not meant to replace HR renewal but to compliment and meant for simple transactions instead of having transactions like creating a ORG UNIT etc.
Anyhow, we have seen many customers built there own fiori apps for everything to replace their HCM frontend ! above article which you found is correct , where in we delivered a launchpad for HR renewal landing pages
WD ABAP render better on desktop as HR RENEWAL 2,0 (in its latest iteration too) currently is a mix of WDA and SAPUI5 .
So coming to your question, probably you can use above launchpad to call your fiori apps?
yes you can add via fiori catalogs in the landing page too
You can read here more
