TOS leverages a glue script that automatically generates reverse DNS records for the resolver kresd | unbound and thus router clients should be accessible accordingly.
That said the glue script works only with dnsmasq as DHCP server and neglects odhcpd however.
Moreover, OpenWrt (and subsequent TOS) deploys a hybrid DHCP server setup out of the box:
dnsmasq for DHCPv4
odhcpd for DHCPv6
It is possible however to utilise either, dnsmasq or odhcpd entirely for both DHCPv4|6.
If not mistaken the governing entries in /etc/config/dhcp for dnsmaq should be something like:
option local '/to.lan/'
option domain 'to.lan'