There's no way any of that would be allowed today.
Wanna bet?
You've forgotten all the not-Trek cameos in the much later "Khan Noonien Singh" trilogy. And even Vaslovik ("The Questor Tapes") in "Immortal Coil". Some of Worf's holodeck opponents have been in-jokes, too. Even Therin Park, New Therin Park, Shantherin th'Clane and the Andorian warship
Therin are more obvious in-jokes for people who've seen "Starship Exeter: The Savage Empire" fan film.
The time period in which in-joke guest stars and references were frowned upon was the 1986-1991 period, when Richard Arnold was vetting the manuscripts. And, even then, he missed a few of Peter David's, such as Arnold's own name on a tombstone. But even PAD managed to squeeze in some "Bloom County" cameos that were approved.