Sorry Alex, that's not what it means.
You first need to understand how a partition is defined on a HDD, and secondly what Ustealth is really doing.
How partition table are defined:
Up to 4 primary partitions can be defined in a "partition table" located on Sector 0 of any storage device (hdd, sd card, etc.)
this table is optional, some device could have no partition table at all, and just be raw data (for example, the WiiU HDD format doesn't have a partition table, because the WiiU doesn't need partitions, the drive is reserved entirely to the WiiU's needs).
So, to know if a partition table is present or not present on a storage device, partition tables have "signatures".
I said "tables", because there are currently 2 different partition table format : MBR (old, 32 bit) and GPT (new, 64 bit).
both MBR and GPT table have the same signature, so it's easier to work with either format.
The signature of a partition table is a unique and fixed value located at byte 510 of the sector 0 : 0x55AA
How the WiiU is working ?
Like I said, the WiiU doesn't use partitions, so it formats the FULL drive's sectors, including sector 0.
If the WiiU detects the signature "0x55AA" on sector 0, then it prompts the user to format the drive to WiiU Format.
How Ustealth work ?
Ustealth only alter the partition table signature to appear like no partition table is present.
Ustealth replace 0x55AA to 0x55AB (or swap it back to 0x55AA if needed)
Ustealth does NOT change anything else, keeping the defined partition information on sector 0 intact and readable.
It also, or course, doesn't touch the partition's data itself (all your partition's data are untouched, and still readable, your files are there).
Usteath does not HIDE partitions, it hides the partition table !
Why some homebrew are working, and some are not?
Some homebrew are checking if the signature is present before loading the partitions defined into the table (up to 4 primary partitions can be defined on a partition table).
Some homebrew are NOT checking if the signature is present, and just look at the location where the partitions are defined.
Homebrew which are not checking the signature are working natively with Ustealth'd drives.
Homebrew which are checking the partition signature BEFORE looking at the existing partitions need a sources edit and recompile to allow BOTH 0x55AA and 0x55AB as compatible signature.
Your computer and all other devices (music player, etc.) will not work with that drive if they check the table signature as they expect 0x55AA, that's why your computer tells you the drive is not formatted. it doesn't recognize the partition table, doesn't even try to see if there are partitions on it.
d2x's FAT library, which is used by "NAND redirection to FAT32 partition" (the emuNAND feature) needed that signature patch to allow 0x55AB as acceptable signature to mount the FAT32 partition where your emuNAND folder is located.
it means that it works ONLY when d2x FAT library is the ONLY used element which is checking the partition table signature, and ONLY when d2x is in use.
that patch was/is not needed when you play a wii game (because it uses WBFS library, and doesn't care about partitions nor tables, it reads raw sectors). The patch was needed only to make emuNAND compatible with altered (wrong) table signature.
Most homebrew are NOT using d2x, they are using IOS58 (which doesn't care at all about partition table or signature).
if a homebrew is not compatible, it's because it's using homebrew SDK (DevkitPro LigOGC's) FAT library without the patch, OR that the homebrew is checking the signature.
To make homebrew compatible you need two things :
1. the homebrew itself must NOT check the signature, or accept 0x55AB as compatible signature
AND
2. doesn't use the LibOGC fat32 library, or use the patched version.
d2x has nothing to do with homebrew compatibility, and even if the homebrew used a patched d2x cIOS slot, it will not fix the detection problem, because the homebrew or the SDK is checking the signature, not d2x.
d2x patch didn't fix homebrew compatibility, it fixed a "d2x internal feature".
PS : I might use that as base for my Wii hacking guide to explain what Ustealth is and how it works. ... one day.
with better explanation and pictures maybe.