1. Are these data and pcitures signals sent over the radio network more difficult to intercept/jam than voice signals?
Yes. With encryption and error protected coding, the data terminal would be practically impossible to intercept and difficult to jam. However, voice also can go in the same channel, in digitized form. If the comparison is with the traditional radio, this mode of communication is several orders of magnitude better.
2. As a related question, would radio 'silence' be maintained even if such text data signals are sent/received?
It depends. For text, the duration of the radio burst would be very short. An SMS like phrase can be transmitted in matter of milliseconds, and can be encoded to look like a noise pulse. But sending a picture will take more time, and radio signal will be present for that duration.
3. Is it a simple matter for two platoons, say, to communicate between themselves over this network as opposed to sending their data back to the company and then being appraised of each other's situations?
The range of the handheld units would be tens of kilometres, depending upon terrain. Technologically, it makes no difference whether the communication is between two field units or to a central location. So, I would imagine they will actually do that. there is an advantage too. If one unit is in a forward position and out of range of the command, another unit can relay info.
The technologies for this platform are well established and well within the capabilities. All we need from outside are the hardware parts :-( (processor, memory, comm ASIC, LCD panel etc).