Yes it looks good but a web app can be installed easily on a nethserver if you use an Ibay. Moreover if you install the backup-data module, then mysqldb and the web folder will be saved. It seems that a web installer exists and the piwigo can handle easily updates. Except if the rpm builder brings a lot of customisations and specific settings, I’m not sure that a rpm is the good answer to the issue raised.
Indeed, I think that a detailed howto will be better than a rpm