Yes, that’s fine. So you have an int which represents which material is applied to something in your game.
When you load that int from the save game, you can then look it up in your array of materials and apply the correct material 
EDIT: But wait… If you have, like, 3 meshes you’ll be putting materials on, you need 3 places to save.
You can either have 3 variables, like mat1, mat2 and mat3.
Or you can have an array called something like MyMaterials. It’s just an array of ints, and you put the ints representing the material into that array in the save game.
Do you get it?..