It's probable that drug dealers could use this, but there's a bit of a marketing hurdle if they do decide to go that route. Can you imagine the awkwardness of explaining that you want funds received through Twitter? It's a nightmare since twitter is a public arena and doesn't even use E2E encryption for its DMs, so police can have a nose at your convos.

The drug dealer could already use Venmo or CashApp or Paypal or a hundred other apps. Twitter isn't adding anything new.

Then gets mixed up who paid and who didn’t

A drug dealer could also get cheese from their customers instead of cash. Would that make sense? About as much as using twitter tips, I guess.

It would be a (flimsy) excuse for you to pay them, when in fact you are paying them for drugs.

Dealers who operate at a scale where twitter tips or venmo are viable payment methods are not operating at a scale where they'd need any excuses.