Yeah, the comic doesn't mention Orcus.
But here we go, "Return to the Tomb of Horrors" from Dragon #249 says this:
"While alive, Acererak built an unholy temple to a now deceased power. When the project neared completion, he slew every worker, excavator, and consecrating priest who had assisted in the temple’s construction."
Okay, they don't mention the name of this power, but anyone who has read Dead Gods should be able to guess who it was. This article was from 1998, and Orcus wouldn't be officially resurrected until 2001's Manual of the Planes.
The Dragon article goes on to the note that the result of Acererak's temple-building was the classic Tomb of Horrors module. Area 14 of the Tomb of Horrors is the Chapel of Evil (and here I'm quoting from the original Tomb of Horrors, page 5), "obviously some sort of temple area - there are scenes of normal life painted on the walls, but the people have rotting flesh, skeletal hands, worms eating them, etc." Yeah, this is a temple of Orcus. I don't know how to explain the "faint aura of good detected," unless the temple of Orcus was formerly a temple to some good deity, now defiled.
The introduction to the "City That Waits" section mentioned by Tharian above notes that Orcus created the demiplane of Moil and then "never came again to the city, for he was slain by Kiaransalee, drow goddess of vengeance, and passed from the knowledge of both gods and men."
Acererak "had discovered its existences through his researches when he was still a breathing man. With its creator gone and its inhabitants dead, Acererak claimed it as his own."
Okay, the concrete connection between Acererak and Orcus is in the journal booklet, page 7:
"Acererak found the means to study sorcery and evil necromancy. Being an entity of enchanted lineage himself, these arts came quickly to him, and he soon became a master of spells. In the text, there was also a reference to someone or something called Tenebrous, to which Acererak owed much of his power, but the details are unfortunately not explained."
Note that Acererak was both a magic user and a cleric (1st edition Tomb of Horrors, page 10), so it seems safe to assume he was a cleric of Orcus.
If you don't think it's safe, there's this quote from Bruce Cordell in Dragon #371 (page 65):
"Bruce: I developed an entire backstory for Acererak that wasn’t included the original Tomb of Horrors by Gary Gygax for two reasons. One, Return to the Tomb of Horrors was a boxed set and I had room to do so, and two, because discovering Acererak’s backstory and future plans set the stage for all that occurred in RtToH. I developed his origins as a persecuted tiefling child to his development as a wizard and priest of Orcus, to his creation of his tomb that was actually a test to winnow souls, to his final Fortress of Conclusion."
And of course Dead Gods credits Acererak in part for bringing Tenebrous back from death into undeath (page 6): "Forces - possibly inadvertant, possibly not - conspired to bring the dead god back. Somewhere in a tiny demiplane known as the City That Waits, a number of the former Abyssal lord's worshipers suddenly awoke from their eternal slumber. Somewhere on the Prime, a lich named Acererak stirred up the dark suspension of the Negative Energy Plane with a barmy scheme."
Anyway, to sum up the connections:
1. Acererak owes Orcus much for his rise to power (Journal booklet, page 7). He was a cleric of Orcus (Tomb of Horrors (1978), page 10; Dragon #371, page 65).
2. Acererak built a temple to Orcus, killing every worker and sealing them within. This would become his Tomb of Horrors. The temple area is area 14 of the classic tomb, and the workers are sealed in the Undertomb below (as detailed in Dragon #249, page 38-39).
3. Orcus created the City That Waits. Acererak made the City That Waits his own abode after Orcus's death (Adventure booklet, page 56).
4. Acererak's tampering with the Negative Energy Plane, along with his waking the undead in the City That Waits and the last prayers of Quah-Nomag, brought Orcus back to an undead shadow of his former self (Dead Gods, page 6).
