The other possibility I thought of was Michael Keaton, since he was Beetlejuice, though that's not really like Bat-Mite.
As to the WW copyright issue, a lot of this is supposition based on circumstantial evidence, but here's what I've put together over the years:
1941 - William Marston creates Wonder Woman and leases the rights to National Comics (a sister-company to Detective Comics which was folded into DC later). Under this arrangement, which persisted after Marston's death in 1947, when the rights passed to his wife Elizabeth and the third part of their menage a trois, Olive Byrne, DC would have the right to Wonder Woman so long as they published four issues of her comic per year (which is, incidentally, why she was the third and only superhero to keep her title during le grand noirceur that was the 1950s). Under this deal, likewise, she can make guest appearances elsewhere, pending clearance from the owners.
1986 - Continuity reboot, and while George Perez and co. are working on the new volume, they're in danger of losing the copyright, so Kurt Busiek (then a newcomer) is drafted with doing a four-issue out-of-continuity miniseries to fill the gap and keep the rights in play. The new Wonder Woman volume launches in 1987.
1988 - Wonder Woman makes her final guest appearance on another show when she appears in an episode of the Ruby Spears-produced Superboy cartoon of that period.
Now, according to Kurt Busiek in an interview he gave once, at some point after the 1986 miniseries he wrote, DC cut a deal with the Marston estate to permanently sell the rights to Wonder Woman to DC. From that point on, they own the character.
The big speculation, based on circumstantial evidence (and a creator statement, which I'll get to) is that, as a condition of the purchase, perhaps to insure that the character would be treated with respect in other media, the Marstons insisted on a clause where she would not be used as a guest star, only as a star.
2000 - Batman Beyond does a Justice League episode, and they want to use Wonder Woman, but are told that they can't. Paul Dini commented in an interview that there was a bunch of red tape and that they could do a series about her (which they didn't want to), but, for some reason, not as a guest star. Big Barda is substituted for Diana in the episode in question.
2001 - Justice League launches, and, since she's part of the main cast, Diana appears for the first time.
2001-2005 - JL/U runs, and, concurrently, there are several crossovers with Static Shock, the other Timm cartoon of the period; Diana is the only member of the original lineup who does not appear.
2003-2006 - In a rather interesting development, the production team for DC's Teen Titans anime-inspired series is told that they can't use Wonder Girl as a guest star either; Wonder Girl isn't a Marston creation (she dates to the Bob Haney Teen Titans era), so it seems the ban extends to the whole mythos (which makes a certain amount of sense, since she's clearly a derivative).
2007-2008 - The Batman does a fifth season that's almost nothing but JLA guest appearances, and Wonder Woman does not appear (no women at all appear, even, but that's another story).
Based on the timeline of her appearances and Busiek and Dini's statements, the general supposition is that the change in status came with the terms of sale.