I have a PfSense router / FW and a unifi switch / AP and have already disabled all of the broadcast features of the unifi stack.
What I have noticed is that whenever the broadcast flag is set on DHCP requests the PfSense box will not respond to the request. This could either be solved by not sending the flag which seems to be the default for almost all of the other IoT devices I have or just allowing static IP config on the Rachio.
" To work around some clients that cannot accept IP unicast datagrams
before the TCP/IP software is configured as discussed in the previous
paragraph, DHCP uses the ‘flags’ field . The leftmost bit is
defined as the BROADCAST (B) flag. The semantics of this flag are
discussed in section 4.1 of this document. The remaining bits of the
flags field are reserved for future use. They MUST be set to zero by
clients and ignored by servers and relay agents. Figure 2 gives the
format of the ‘flags’ field."
I have done packet captures on the pfsense box of these conversations and can confirm the broadcast flag being set as well as the requests being seen by pfsense and the lack of response from pfsense itself.