To control an external scanner from EB using the Barcode API it needs to be connected using the SSI protocol, maybe even the simple COM port protocol, but I'm not sure as I've never worked on that scenario. For sure using HID you cannot control the scanner from EB's Barcode API.
Regarding the cable, you need to check which protocols are supported by the part number you've.
You should be able to use DataWedge to do some test following the device documentation.
The USB cable we have (P/N CBA-U01-S07ZAR) with the DS3508 doesn't work in DataWedge on the VC70 under any of the scanner's USB device types. Regarding whether the USB cable support SSI with the DS3508, I can't find any information to confirm one way or the other. The SSI Programmer's Guide does mention that "Zebra's Simple Serial Interface ... enables decoders (e.g., SE955 scan engine, hand-held scanners, 2D scanners, etc.) to communicate with a serial host". The only mention of "serial host" in the DS3508 product reference is under the "Chapter 7 RS-232 Interface" (for connecting the scanner with an RS-232 host).
Our contact at Zebra is now thinking that we need an RS232 cable (P/N CBA-R49-C09ZAR) rather than a USB cable for this to work on the VC70.
FYI, we received the serial cable today (P/N CBA-R49-C09ZAR) for our DS3508 scanner and I can confirm this works with the barcode API in Enterprise Browser v4 on the VC70. The DS3508 scanner needs to be configured according to the instructions on pg. 2-24 of the VC70 Vehicle Computer Product Reference Guide (the section titled "Connecting a Serial SSI Scanner (LS3408-ER/DS3508-ER) to a Serial Port").
In case anyone finds this information useful, I found the scanner doesn't like being disabled on some screens and then re-enabled on other screens using the EB.Barcode.disable and EB.Barcode.enable functions (for some reason there is a lengthy delay before the scanner is ready after calling EB.Barcode.enable). So instead of doing that, for screens where I don't want the scanner to operate I just call the EB.Barcode.enable function again with the "allDecoders:false" property, which prevents the scanner from recognising any barcodes (effectively disabling it). To re-enable it again, call the EB.Barcode.enable function with the "allDecoders:true" property.