I would suggest using the Call Library Function Node.vi. I'm attaching a document from NI's website entitled "Using External Code in LabVIEW." I would suggest taking a look at this. It's helped me quite a bit in the past. Here are a few important things to watch out for. Initialize the array before you send it to the Call Library Function Node.vi. Also, if you are going to change the size of the array in your DLL, you need to use a CIN instead and use the appropriate CIN functions. This is all explained well in the pdf file, so this should help you out.
J.R. Allen