Cave, who has won Under-20 and 'A' caps for Ireland in recent years, is the province's main addition to the panel that was on duty for last week's win over Connacht.
Cave signed a one-year professional contract with the province last month, after impressing on a development deal and he has performed well in a number of Ulster 'A' games.
The Belfast Harlequins clubman has already played under Williams, coming on as a replacement in Ulster's 20-8 Magners League victory over Llanelli in February.
Meanwhile, Ulster's remaining home Magners League fixtures against Glasgow Warriors and Cardiff have had their dates and kick-off times confirmed.
Ulster's re-fixed interprovincial clash with Munster has also been moved to Wednesday, April 30.
For anyone who was unable to get a ticket for the original Ulster v Munster date in January, there are just under 1000 terrace tickets available to purchase now online at www.ulsterrugby.com or on tel: 02890493222 option 2 (please note, for consistency, any new tickets issued will be dated January 4).
Tickets for Ulster v Glasgow tie, which will be played on Saturday, May 3 (kick-off 3pm), are on sale now. Please click here to buy.
Tickets for the Ulster v Cardiff game (Friday, May 9) will go on sale on Monday, April 21.
ULSTER Squad (v Cardiff Blues): Backs (12) - Paul Marshall, Isaac Boss, Paddy Wallace, Niall O'Connor, Mark McCrea, Darren Cave, Andrew Trimble, Tommy Bowe, Bryn Cunningham, Rob Dewey, Paul Steinmetz, Mark Bartholomeusz.
Forwards (14) - Justin Fitzpatrick, Rory Best (capt), Tom Court, Justin Harrison, Kieron Dawson, Stephen Ferris, Ryan Caldwell, Carlo Del Fava, Matt McCullough, Nigel Brady, Bryan Young, Neil Best, Roger Wilson, Stuart Philpott.