No, a DEXA scan is not a good tool to detect osteoarthritis.
Bodyscan performs only body scans, not bone density scans.
DEXA bone scans (which Bodyscan does not provide) are designed to detect low bone density (osteopenia and osteoporosis), whereas osteoarthritis is about the joints between the bones. They are often confused as they can often occur together.
If you are worried about osteoarthritis you should seek a specialist.