As hype swarms in on the potential approval of the first U.S. spot bitcoin exchange-traded fund in the coming days, another lingering, tangential component remains — Coinbase's legal battle with the Securities and Exchange Commission.

If the SEC decides to approve a spot bitcoin ETF, as some analysts expect, Coinbase would have a substantial role by providing surveillance and custody services for major financial firms such as BlackRock, Franklin Templeton and Grayscale Investments. It recently hired a new executive to head its custody department. 

The developments would come as the exchange has been embroiled in the separate legal battle with the SEC over the past year after the agency accused it of operating as an unregistered exchange, broker and clearing agency. Coinbase has …