Being a raw feeder is one thing, being a carrion eater is another thing all together. That mouse sat over night in your snake's cage decomposing and breaking down. Now you've re-frozen that tissue and if you re-thaw to give it to the cat it's that much more damaged. I just don't see how that can be a good idea. Cats who eat raw, by and large, eat fresh kills. That mouse in your freezer doesn't qualify. Will your cat eat it? Yeah, probably, but that doesn't make it good for the cat. Most likely, nothing will go wrong, but is it worth the risk?
There has long been a rule of thumb in the snake keeping community that if a snake were to refuse a F/T, you never re-freeze it, you just toss it out. Generally, rules of thumb get that way for a reason.
I'm a very firm believer in personal liberty, and you certainly have the right to feed your cat anything you see fit, I just don't think feeding that mouse would be safe.