Cleaning Sand with Gravel Vaccum

Yes you can... I usually only vacuum my sand once a month & only parts I can easily reach. I usually stick the tip of the vac down in the sand a bit, maybe 1/2"-1".

Sand substrate can be vacuumed, but there are a couple of little tricks that can help you not to lose too much sand.
If you siphon the water into a bucket then lift the bucket up, perhaps sit it on a chair. The idea is that the water will not fall so far, and this will slow the siphon, and your vacuum will pick up less sand when the water flow is slower.
Another trick is to keep one hand around the tubing, ready to pinch it off if the larger part of the vacuum picks up too much sand. You do not need to totally stop the flow, just slow it until the sand drops. (This is an interesting way to re-landscape: Pick up the sand from deep areas, then release it in areas that need a little sand.)
Last little trick: Put a nylon stocking over the gravel vac. This will reduce the amount of sand that is picked up. Of course only the finest debris will enter the siphon, as well, so this would not help if you knew there was larger stuff you were trying to remove.

I have some nice fresh white sand in my (DIY'd) Betta Barracks, so this question is of interest to me... I had read somewhere (maybe even here) that something like a chopstick or similar secured by rubber band to the vac. tube with a rubber band is a good idea. The chopstick (or what have you) would extend beyond the tube by an inch or so, and is used to gently stir through the sand, churning up all the debris/detritis...

Would this be OK?

The chopstick idea sounds good. I gotta try that on the front part of my tank to get the stuff under the small substate next to the glass.

Tried it and it worked great especially with a small gravel cleaner I have that only has a small suction so I can take my time and only take out a minimum of water for the front of a 50 gallon tank. Loosened the blue green algae on the top part of the substrate against the glass and sucked it up without any of the light substrate.