Nebraska Game & Parks operate on a repeater frequency of 159.330 statewide. The the closest repeaters to you look like they are in Carroll and O'Neill. The Game & Parks system is very old. They use an audible tone pulse system to bring up the repeaters (like medical units use when calling hospitals on 39.820).
The are licensed to a bunch of frequencies, but I have only heard the 3 with comments used:
151.205 - State Wide Repeater Input Frequency
151.385 - Aircraft to Mobile (In the past I have heard aircraft chasing poachers in the night hours)
159.330 - State Wide Repeater Output Freq
Game & Parks Units are identified with a 7XX number. In addition to VHF, game and parks vehicles are often equipped with low band. When I lived in rural Nebraska, Game & Parks would often be heard on 39.900 in addition to local agency VHF repeaters (Sherman Co. 155.895, Howard Co. 155.775, and Valley Co. 155.490).
In Lincoln, Game & Parks has a rarely used talkgroup on the Lancaster County Trunked system. They have a few county issued handhelds.
About a year ago, when KOLN outfitted their tower by Beaver Crossing with a digital TV antenna, they kicked all land mobile radio transmitters off of their tower. Prior to that time, I would often hear Game & Parks talking on the Beaver Crossing 159.330 repeater with a callsign of KAO848. Since then, I have not heard any activity on the VHF Game & Parks frequencies.
As far as the NSP 450mhz frequencies....these were used for control frequencies for their remote 42mhz base systems. These are gradually being phased out due to changes in FCC licensing that now allows businesses to be licensed on these frequencies that were once reserved as fixed control frequencies. These businesses have caused interference issues, so NSP is moving to phone lines to control remote bases. You will still find some of the 450mhz freqs in use. For example, last time I monitored them, Lincoln still used 452.500 to control the Auburn tower and 457.150 to control the Mead tower.