I don't see why any vendor would have an issue using Privinote if it makes you feel more secure.
Re tracking of BTC, there are far worse things being done with Bitcoin than buying a bit of weed off the internet. Don't worry about it. If it makes you feel better chuck them through a tumbler but just be careful not to get scammed.
It's always good to be careful, but i think you might be worrying a bit too much. In the grand scheme of things, buying a few grams of puff from here is nowhere near the main concern for any authorities monitoring the internet or bitcoin.
Just my 2p.