Donlass,
Without at least some specifics, addressing your question is rather difficult.
What kind of aircraft? Which crash? What sort of misunderstanding? Any details at all.
Certain hydraulic fluids are flammable, certain aren't. Generally there's very little hydraulic fluid in the airplane, not enough significantly contribute to a post-crash fire. In the B747, for example, we've got only a few gallons of hydraulic fluid for the entire airplane, spread mostly through small hydraulic lines in different areas...hardly enough to pool and make a hazard, let alone a fire hazard. In fact, our hydraulic fluid, called skydrol, is very difficult to ignite; even a mist sprayed over a lighted torch won't ignite it.
Other hydraulic fluids used in some airplanes, namely H5606 fluid, is flammable...but it's generally not used in large transport category airplanes. You'll find it more in smaller airplanes and corporate type jets and turboprops...still generally in very small quantities.
We carry 230,000 lbs of fuel in the wings, however, and a center tank can hold another 85,000 or more pounds of fuel...more than enough for a significant fire.
The position of the landing gear doesn't have a lot to do with that. If you're asking about a fire on the ground and the landing gear holding the airplane fuselage away from the fire...that won't make much difference. If you're talking about the landing gear protecting the fuel tanks or other fluid storage from the ground, bear in mind that in a crash very often the wings are ruptured and fuel either pours free, or ignites as a mist or when coming in contact with hot engine parts.
Landing gear can be ripped free or bent back, absorbing some impact, but it can also do the same retracted; it serves as a thick, tough barrier to the ground when it's retracted, too. Some older airplanes even left part of the tire sticking out for that very reason.
When making an emergency forced approach and landing, delaying puting out the landing gear is often an important consideration. Extending the landing gear can create substantial drag, meaning the airplane won't glide as far and will descend faster. One wants the lowest possible forward speed, and lowest possible descent rate during a forced landing. Having the gear out can make for a higher rate of descent, resulting in more injury and damage. It may also make it difficult or impossible to achieve a glide to a successful landing. During an all-engine failure, hydraulic pressure may not be available to lower the landing gear or secure it, another important consideration. Also, the crew may be more important with bigger issues of handling the emergency.
A crew may have to decide how to best put the airplane down to minimize damage, but this can include decisions such as using the wings or landing gear to absorb impact energy that would otherwise be transmistted to the fuselage and ultimately to the passengers. There may not be time for putting down landing gear and attending to that function, while one is handling the emergency.
Do you have some specifics? It may be easier to address your question of you have some references or a direction to go.