the reserved IP addresses are 192.168.1.0 and 192.168.1.255.
You cannot assign them to hosts or to the router. The allowed range of IP addresses for your configuration is from 192.168.1.1 to 192.168.1.254.
Also keep in mind the DHCP range, which must not overlap with statically assigned addresses.
(I drafted this and never hit post, but @mbo2o covered most of it:)
Not entirely accurate...I've assigned...it does behave differently, though. Likely because of routers along the path needing upgrade...or the subnet divided in some router along the way (making the 0 or 255 invalid). Why do I say this?
Because I've passed traffic.
Of course, when you assign .0 or .255, the subnet used isn't a /24, and the IP's used still cannot be on a bit boundary of the subnet used (wish is the actual issue).
.0 is not a reserved address in IPv4. It may be that OpenWRT won't accept it, but it is a perfectly valid IPv4 address. If it is a "good choice" for an address is a different question, but it certainly is a valid IPv4 address (as is .255 that is not at the "end" of the net block).