Well I have pretty much come to a conclusion.
In short, yes, it will work (if the reservation already exists). However like so many things from MS there are some caveats since there can be errors if adding a NEW reservation outside of the address pool.
It seems the best method is to utilize exclusion zones on your address pool to limit what range of addresses are automatically assigned via DHCP.
Straight from this Microsoft KB
- You may create a reservation in any scope range. This can include
- You may create a reservation in a subnet range even
if the reservation falls outside the actual scope Start and End
addresses for that subnet.
- You cannot create reservations outside the subnet range of any of
your existing scopes.
Using exclusion ranges is preferred because there is a known error that can occur if you attempt to add a reservation that is outside the range:
"The specified DHCP client is not a reserved client"
To avoid this potential issue, use exclusion ranges as defined in this article
If, for some reason, you do not want to/can't set up exclusion ranges, and can't add a reservation outside the address pool, then this hotfix is to solve that bug.
In conclusion / Solution Summary:
Since MS states that reservations CAN be used and assigned WITHIN an exclusion range, what I will do is leave my address pool as-is, and I'll configure the exclusion range 10.10.5.2 - 10.10.5.239
Here is my final config:
Scope = 10.10.5.0/24
Address pool = 10.10.5.10 - 10.10.5.254
Exclusion Range = 10.10.5.10 - 10.10.5.239
This will leave my desired range of 10.10.5.240 - 10.10.5.254 for auto-assigned DHCP addresses and will avoid any potential errors explained above.