Can a pilot use ILS when cleared for a visual approach?
Yes, the localiser, ILS glideslope, and/or GPS-generated glidepath are still used as a reference during the visual approach. Sometimes the visual glideslope indicators (like VASI or PAPI) are either inoperative or not available. (Interestingly, the visual indicators and instrument-generated glidepaths are sometimes not coincident.)

Pilots sometimes choose to leave the autopilot engaged during such an approach. Some Charted Visual Flight Procedures (like the FMS Bridge Visual 28R at SFO) lend themselves to leaving the autopilot engaged for almost the entire approach. In addition, some operators may stipulate that autopilot use is mandatory.