To answer your question directly, no Steam doesn't notify the purchaser that the game needs Oracle's Java Runtime Environment installed to play the game. That's because there shouldshouldn't be any need to, any game that has a dependency on the JRE will download and install it as part of the normal Steam installation procedure. This is no different than games that have dependencies on Microsoft's Visual Studio, DirectX or .NET runtime. There is even a standard JRE depot that you can use.
That said, I personally refuse to buy or install any game that dependent on Oracle's JRE. I don't want to have to deal with that nonsense. An alternative route would follow Minecraft's lead an include a Java VM as part of the game itself. That is, instead of installing a VM for all Java applications on the machine to use, like with the Oracle JRE, you install a VM side-by-side your game that only your game uses. I don't think you can do this with the Oracle JRE, I believe Minecraft uses one based on OpenJDK.
On the other hand, if you're just starting out, you should probably take the easy route and use the standard Oracle JRE install, and just accept some people won't like that.