Is it OK to leave some part out of the schematic if noted?
A schematic is an abstraction of the real circuit. We use abstractions because we want to communicate something to other people (including our future self). If what you want to tell to other people about your circuit does not involve the fuse, then it is fine to leave it out.

But if you want to use your schematic as input for making a PCB and you want the fuse on the PCB, then it is silly to leave it out in the schematic.

So it all about the intented use of your schematic.