Yes and no. Any law enforcement officer can search a vehicle, without warrant, if they have probable cause to believe it holds evidence of a crime. However, they must show the evidence was at risk of being destroyed due to the mobility of the vehicle. In other words, if the driver is in jail and the vehicle impounded, the courts would very likely hold a warrantless search as unconstitutional.
The same holds true for any game warden. The level of probable cause they must show to conduct a warrantless search of the vehicle, or any of the other items listed above, is the same threshold they would need to achieve in order to obtain a search warrant in the first place. So, warrantless, yes, but clearly not as ominous as that may appear on the surface. Any evidentiary items seized and used in prosecution would be subject to suppression by the defense if the prosecution failed to show a sufficient level of probable cause.
It is worth noting the courts continue to scrutinize warrantless searches, and are not allowing them simply because they were in the past. Every time a warrantless search is done, the officer must show the exigency present that compelled them to conduct the search without taking the time to apply for and receive a search warrant.
Putting this all into context, say you get checked by a game warden in the field. He asks you (required by law in most states to submit to a field inspection and present all game and/or fish) to see your game, to which you reply you have none. Acting on a hunch, he tosses your truck and finds an illegal bobcat under the rear passenger seat. You get charged for the crime.
Any defense attorney worth his/her salt will immediately attack the warrantless search. If the warden cannot articulate the elements of probable cause that compelled him to search your truck (acting on a hunch or your gut is not probable cause), the entire case is tossed. Now, if he/she can say they saw blood on your pants, noticed bobcat hair on the edge of the door, your vehicle matched the description of someone shooting a closed season bobcat, etc., you might be in deep shit.
Lastly, tents are more likely than not to fall under the definition of a domicile, and as such any officer would be required to apply for and receive a search warrant to enter into them and look for evidence. If I'm spending 10 days in the field in my wall tent, you can darned well bet I consider that my temporary domicile. The appellate courts have viewed a tent similar to a hotel room, in that both carry an enhanced expectation of privacy.
