Could I use long grain brown rice instead of short grain?

You can definitely make it with another type of rice. Rice porridge that I've had in restaurants, for example, is usually made with jasmine rice, and I've also made rice porridge at home with a wild rice blend. (see here: https://recordsintheden.com/2016/08/28/676/)

The difference will be in the amount of water you use. For example, short grain brown rice takes more water and makes a thicker porridge while jasmine can tend to be soupier. Either way it should work out.

I used long grain brown rice with no adjustments (except halving the recipe) and it worked well.

I think you should be able to make this with long grain rice. You may want to add less water and not cook for as long as specified in the recipe.