"Jerry Capeci, for one, wrote in "Murder Machine" that Roy had grown exceedingly paranoid and had taken to tape recording his own conversations -- Capeci never wrote that Roy had flipped or that Roy was making tapes for anyone but himself."

Hard to say what the real reason for the tape recorder was.
He could have been making future tapes as "insurance" in case he got busted,or he coulda been making tapes to blackmail business associates in order to try to buy more time,or he coulda been hoping to catch his murder on tape so the hitters could get caught.