While 575 isn't that much, I would err on the side of being overly supportive. Be it bricks, blocks, boards, or a house jack, extra support under the safe won't hurt. It doesn't even have to be tight, but just be there is there is a sag or settle issue.
Actually, the best thing you can do is to get under the house and actually see how well things are supported BEFORE putting in the safe and see what condition the wood is in. I once saw the result of a large TV/Stereo entertainment center try to fall through the floor at the wall. There was no reason that should have happened had everything been okay. As it turned out, the wall the entertainment center was against was a wall for the shower area of the bathroom. Unbeknownst to anyone, there was leakage from the shower resulting the rotting of a 2x6 beam and when the beam let go, the entertainment center sunk down about 4" as the floor tried to collapse.
In crawling under houses, it can be easy to spot the bathrooms and kitchen areas even when you don't see pipes and that is because the wood will be water stained. There is almost always some leakage somewhere at some time.
The other thing is that not all home are piered the same and if it is an older home, the piering may be creative. I have been under homes where gravity was the primary force keeping a beam on a stack of bricks. The only problem was that through normal house movements such as clay shrink and swell, the stack of bricks managed to topple over somewhere along the way. They were no longer supporting the beam.
We have a weekend house. While getting it ready for winter, I crawled under it for the first time. It was an old farm house that no doubt would never have passed an inspection in the city. The builder apparently used stacked natural rocks (limestone, sort of tabular) as center supports. While there is evidence that more supports were in use than are there now, I could not imagine where the rocks would have gone...until I realized that it is quite likely the front sideway is actually paved by tabular limestone blocks. Some moron previous owner decided the rocks were not needed under the house and put them to use as a sidewalk!
Moral of the stories for gun safes? While the safe may not be huge or super heavy, it would be in your best interest to take a look under the house and see just what condition everything is in. Things may be fine. Things may be fine but you would be happier with some additional support after you check out things. Or, your intended location may have some issues that need to be address or maybe you need to seek another location. After seeing the entertainment center trying to fall through the floor, I think I would avoid putting the safe against a wall that had a bathroom or kitchen on the other side.
Besides, once in a while you find some cool stuff under houses...and it is in your best interest to wear a repirator.