You can try to load the file as a ClearCanvas.Dicom.DicomFile, and if it doesn't throw exceptions then the file is at least in DICOM part 10 format (there's not much validation available for whether or not the contents of the file is valid for a particular given SOP class - this is typically done by the code consuming the file).
If you're not going to be consuming pixel data, this following snippet should work; otherwise, take out that option to the Load method.
bool isValid = true;
DicomFile dcf = new DicomFile(path);
isValid = false;
Hope this helps,