I know some other people have done this, and I think it's a great idea. Tyrlandi can make her information hinge on slaughtering the current bosses at the Porphyry House, where they use wolverines and ugly aberrations as prostitutes. But a couple of things about that adventure path confuse me.
1. The serpents are using polymorph on animals and aberrations with intelligence of 1 and 2. So they may look like beautiful courtesans or whatever, but would they know how to act in bed? Maybe I missed something. Seems like it would require some sort of dominate spell.
2. I suppose you could ask a customer if they care about having a courtesan who can talk, and if they do, get a harpy or something with intelligence. The party might get a kick of NPCs who don't care if a prostitute is mute.
3. My characters are 14th or 15th level. I think the key will be using a DC save high enough that some people in the party will be half fiends after the demon's breath. Otherwise, it will just be cakewalk.
4. Maybe I could also make it a hostage situation - "Stand down, or another participant in the orgy dies."
Porphyry House (PH) is an excellent additon to Serpents of Scuttlecove (SoSC). I know this from personal experience. Things to keep in mind:
(1) What system are you running? I believe PH is designed for 3.0, so if you're running a 3.5 campaign, the adventure is going to be underpowered. If you're running Pathfinder, it's going to be even more heinously underpowered.
(2) Along those lines, PH is designed for level 10, iirc, so at 14th - 15th level, whichever system you're running, your characters are going to be egregiously prepared to tackle this adventure. Keep in mind that your players will have access to spells that the module doesn't anticipate. They might make certain portions of the adventure (or the whole thing) that cakewalk about which you're worried.
(3) PH is R-rated (and, depending on the DM, can easily slide into an X-rating). How old/mature are your players? The depravity of the adventure (PH) could easily sidetrack your players from accomplishing the mission of the campaign (SoSC).
(4) Tie-In. Scuttlecove is an obvious setting/location for Porphyry House, but how does PH connect to the campaign. You'll need to place key information/people from SoSC in PH or else PH just become a side-trek.
My players are all over 35, so I wasn't worried about the X rating. It did work out, though I'm not sure it was their favorite part. I beefed up the stats a little for 3.5, but it was still too easy. One of my players shot an arrow after the Yuan Til had swords to the necks of the innocent orgiasts, resulting in a lot of hostages dying (I took away XP from him).
The tie in was that Tyrlandi wouldn't disclose the location of Harliss until they took over the PH. My players also negotiated to be her business partners.