even after being acquired, a company doesn't absolve of it's obligations to honour contracts (verbal or written).
If Ellison decides to retract said IP waiver, he would have to publically say so, and because the existing IP waiver Musk have provided doesn't seem to include any terms such as termination, i would assume it's an indefinite and perpetual waiver. Hence, Ellison will have to sue (and probably lose) to have existing usages of said IP to be discontinued.
Tell that to Google, who used the verbal agreement of the Sun CEO that they could use the Java API. Taken over by Oracle and now they are sued over it.
Think what you want about Elon, but he made the pledge openly and directly I think that means something.