ip managment for ap wds slave

I, i have some ap in wds slave mode and i use pppoe for my user, i need to add ip to wlan interface for management purpose (nagios checker), i have think to add some firewall rules for block all traffic from wlan except traffic to nagios server ip destination… It’s a secure way ?
can i use other solution ? I’ll prefer to not add ip to my pppoe server interface

Thanks

FR4