Okay, from what I seeing in the database on this site if you want to monitor all of the public safety agencies in both counties you will need a scanner that will recieve trunked digital APCO Project 25 Phase II transmissions. There are currently only a few of those.
This is a list of the currently available scanners that will receive that type of system:
GRE PSR-800 (with firmware upgrade, not out of the box)
Radio Shack Pro-668
Uniden BCD325P2, BCD436HP, BCD536HP, BCD996P2, HomePatrol-2
Whistler WS1080, WS1088, WS1095, WS1098, TRX-1, TRX-2
See this page for more information:
APCO Project 25 - The RadioReference Wiki
Here is a bit of information about each system:
Nebraska State Patrol uses the following system and you will need a scanner that does APCO Project 25 phase I which can be done by all of the above scanners and many others:
Nebraska State Radio System Trunking System, Statewide, Nebraska - Scanner Frequencies
It looks like their channels are not encrypted and they have repeater sites statewide.
Offut uses an APCO P25 system but it looks like all their talkgroups are encrypted (note the letter E in the mode column) so you will not be able to hear the voices.
Offutt Air Force Base Trunking System, Bellevue, Nebraska - Scanner Frequencies
It looks like most if not all of the public safety agencies in Douglas County are on one system and it appears that only a few channels are encrypted like narcotics and such. You will need a scanner that does APCO Project 25 Phase II
http://www.radioreference.com/apps/db/?sid=2361
And for Sarpy County it looks like they use a system that is mixed digital and analog so you will need a scanner that does APCO P25.
http://www.radioreference.com/apps/db/?sid=622