The problem you are going to run into is the quality of the driver that was created for the USB-232 converter you get. If you purchase a really cheap one from a no name vendor, you should expect cheap quality and it is possible that you will run into problems. Some of the USB-232 converters out there don't support all of the functionality found in the built in ports and this can cause problems with LabVIEW, because it is going to try and set every property when it opens a port. If the port doesn't support every property that LV is trying to set, then LabVIEW will fail to open the port.
I am a little biased, but if you want something that is reliable and that is just going to work with any application and will support all the attributes of a built in serial port and more, than I would suggest trying out the NI USB-232. The one port version is really small and works great. They are extremely reliable as well. As a side note the NI Serial Troubleshooting Wizard ships the NI Serial Driver and it can only be used with NI Serial hardware, because it is just making calls into our driver looking for NI ports making sure that the proper resources are allocated and that it is able to communicate with the transceivers.
I hope this helps out.
Josh Prewitt
National Instruments