No, they can not. The emulator can only handle one of the Motorola 68000 CPUs and the Zilog Z-80a processors. SegaCD had a custom GPU, additional audio channels, and a faster 68000 CPU.

What you said is very false. Mega CD in fact has no GPU (or as most people would call it, VDP), but in fact relies in the Mega Drive VDP. 32X is the one which has its own VDP. Furthermore its good to make the distinction between sound channels, and just sound chips. Mega CD has another sound chip, as well as some software playback of digital media (such as MP3's). The really dicky part about emulating the Mega CD is synchronization of the two CPU's properly, correctly emulating the CD drive, as well as the messy hardware implementation of the machine as a whole. There are not many emulators attempting to do this, and the ones which do try, do an absolutely terrible mess of a job. To the point they might as well not have it at all. Similar issues arise with 32X too, but on a much larger and more facepalm-inducing levels. I doubt SEGA will think its worth the effort to try and support either pieces of hardware, as they are too much pain in the ass for the likely small usage in the end. Both from mods and actual games.

It did have a GPU/DAC/Custom ASIC, otherwise it would not have been able to render Mode 7 like scaling and rotation visual effects for sprites in the sweet way it could, and render up to 960 polygons a second.
References:
http://www.retrodev.com/scdgfx.txt
https://commons.wikimedia.org/wiki/File:Ic-photo-Sega--315-5632--(Sega_CD-GPU).jpg
-- An excerpt from the MEGA-CD development manual from Sega, page 43, says:
"( 3) Graphical Numeric Processing Function
The MEGA-CD incorporates a built-in graphics numeric processing chip to strengthen the graphics capabilities of the system. This chip is structurally linked to the word RAM area and all data transfers involving this chip take place in word RAM. The chip supports coordinate conversion functions such as rotation, enlargement and reduction and a full graphics function that allows images to be displayed by specifying each individual dnt." The rest of the manual has good information.

The difference between VDP and the ASIC processor is, that VDP still handles 100% of the graphics of the Mega Drive, but that ASIC can aid in scaling, rotation and 3D graphics. This, unlike a GPU or VDP, does directly not do any graphics processing nor is connected to any type of VRAM or graphics memory. It instead connects to the memory used by the master or slave 68k and lets it deal with passing the graphics further to the VDP for actual graphics processing. The ASIC processor is no more than a chip that the programmer can utilize to what the hell they wish, but is most usable for graphics-related processing. But yes it would add yet another layer of complication as far as creating emulation core for it and keeping it in sync. This already was huge pain in the ass in physical machines for programmers, it would be even worse for emulation.

Zip up your pants. This was supposed to be a simple question, not a disection of SEGA archetecture.

Nah, there are emulators out there that run Sega CD games (a good amount) just fine. Whether Sega would ever contact those developers and work with them to make an official one for the HUB here, who knows.

Originally posted by Big Boss:

Sorry for spammin' 2 topics but they don't really seem related. Can Genesis CD ROMs work as well? Lunar 1 and 2, Shining Force CD, lots of good games... D: