No, any fluid will transmit the pressure without diminishing it.
Correct, the increased atmospheric pressure would still be transmitted to all the individual components, BUT would be equalized throughout the entire volume of the device as long as all gas was replaced with liquid or solid material. Versus if you just wrapped a vessel with a flexible membrane that trapped interior gas, the compression of that gas at depth would result in inward force around the perimeter, "crushing" the contents.
Essentially, the same effect as how your hand doesn't "feel" any squeeze when exposed to pressure outside your drysuit, since there aren't any gas pockets inside your hand - your skin doesn't squeeze your bones, but with your drysuit if you don't add gas during a descent, your suit vacuum packs your exterior as the interior trapped gas compresses with depth.
I'm 99% certain that if you could replace ALL gas within a electronic device with an intert liquid or gas, and then prevent contact with water, you could take it with you on any reasonable depth and it would still function upon return to the surface. You'd also be voiding the warranty, and probably manage to mess it up with all that silicone or mineral oil. Incidently, if I were to try something like this, I would put the device in a pressure pot, flood it with the oil, and then pull a vacuum to get all the trapped air out of the components and traces. But I wouldn't, juice isn't worth the squeeze as they say.
Also, I'd be concerned that the silicon or oil would interfere with the RF capabilities of the device, similar to how phones and GPS don't work underwater.
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