I want to run multiple VoiceXML applications on the same Voicent Gateway.
I want to be able to use DNIS to choose the application to run. Is that possible?

Yes, you will need Voicent IVR studio for this. It will not require multiple deployed vxml applications.
You simple setup the multiple SIPs (with accounted inbound numbers) in the Gateway. Then use IVR Studio to recognize which line the call is coming from.

To do this first setup multiple SIPs. For this example there will be 4 SIP IDs each utilizing 4 channels.
The setup should look similar to this:

In the Voicent Gateway the line numbers begin with zero. The Voicent Gateway will associate the first SIP ID as channels 0 – 3. The second SIP ID as 4 – 7, and so on.
In IVR Studio individual channels can be selected as entry conditions. For the first child of the root node make an empty prompt called Start. This is required because the root may have only one child. For the first child of the Start prompt, create a prompt element called PhoneNumber1. In this prompt set the entry condition to be defined as __VG__PHONE_LINENO == 0 .
Create a child element of PhoneNumber1 called Phone1Start. You can begin audible prompts in this element.

Next select Start and make the second child element be a GoTo element. Make the entry condition be __VG__PHONE_LINENO == 1. Make the GoTo element point to PhoneStart1. Now whenever channel two is called, it will jump to the first phone menu. Create 2 more GoTo elements that point channels 3 and 4 to the PhoneStart1 element.

Now repeat this method of adding 1 Prompt and 3 GoTos per SIP ID until your IVR call flow looks like this:

Now use each Phone#Start prompt as the root of each different lines individual phone menu. Remember to pay close attention to the amount of SIP IDs and the amount of channels associated with each one.