Residency for your audio and residency for your prospect data are two separate questions, and most vendors answer only the first. An outbound tool hosted in Frankfurt that enriches contacts through a US data broker has not solved your problem. It has moved it one layer down.
Ask for the sub-processor list in writing, and ask specifically which parties touch prospect records. The answer is reliably longer than the sales deck implies.
Dropcontact is the structurally interesting one. It derives contact data rather than storing and reselling it, which is a materially different legal position from a database lookup. The trade is lower match rates on hard segments, so test it against your worst list rather than your best.