CAN HYDROFLEX SPLASHBAGS GO UNDERWATER A LITTLE BIT?
There's a short answer and a long answer...
Short answer, "no." HydroFlex does not guarantee the splashbags for underwater use to any extent. Bags are sealed around metal hardware and there is an o-ring under the glass in front of the lens, but it's always possible for the customer to puncture the material or split a seam in the course of installing the camera or handling the bag. There is also the cable sleeve that is not sealed and if it is not properly tended, water can easily come in through there.
The long answer is, depending on conditions (such as pool vs ocean, standing on firm bottom vs floating, calm surface vs waves, etc), a production might be able to get away with dipping the bottom of a splashbag few inches under. They would need to be diligent about checking for any water coming in and making sure the camera can't get away from the operator because it definitely wouldn't float long. Make sure zippers are fully closed and no seams splitting along any edges. Make sure the sealing screws in the bottom of the bag have fresh o-rings, and are installed and tightened properly. Make sure the bag isn't being handled roughly especially around the viewfinder where it's possible to tear the material away from the screws holding it together.
Furthermore, the real danger is the slippery slope of "...well, they told us we could take it under a little bit." Then the director says "Can't we just show a little bit of water at the bottom of the frame and look up at the character standing outside of the pool?" And then the back end of the camera is fully underwater.
If everybody is "eyes open" about what it can and can't do, you might get away with it. But to reiterate, HydroFlex does not guarantee the bags to protect your cameras for any amount of submersion whatsoever. That's why we call them "splash” bags. A production takes its own risk when doing so.