The answer for this question depends on whether you do have a OPC Server driver for the specific device or not.
1 - If you have an OPC Server driver for the PLC. Yes, you can use LabVIEW to communicate with the device, LabVIEW is a OPC client and you should have no problem communicating with the OPC Server of your device. Normally hardware manufacturers want to provide OPC Server for their device to increase the hardware connectivity, so you might have one OPC Server for your device.
2 - You don't have an OPC Server for your device. You can still communicate with your device, but it depends on what model you have. National Instruments has a product called "Industrial Automation OPC Servers CD"
http://sine.ni.com/apps/we/nioc.vp?cid=11127〈=US
Th
is is a CD with a set of OPC Servers, and your device might be listed there. For a complete and detailled list of the drivers containned in the CD take a look at this document.
http://www.ni.com/opc/opcservers.htm
I hope it helps
Best Regards
Andre Oliveira