You seem to be confusing the EZ4 and EZ5.
The EZ5 is the DS slot cart from the EZTeam much like the r4, SC ONE, cycloDS and so forth, these days it comes with a GBA slot device called the EZ5 3 in 1 that a good deal of others use to run GBA code.
You can however buy the EZ5 and the 3 in 1 separately.
The EZ5 3 in 1 or more commonly the 3 in 1 has two small areas of memory.
NOR and RAM
NOR is permanent and 256Mbit (32 MByte) in size, takes a while to write to though.
RAM is fairly quick to write to and loses data when the power is turned off. It is only 16 Megabytes but as most roms are that size or smaller it does not matter much.
It comes in GBA cart size and DS lite GBA slot size and has a couple of different colours.
The EZ4 is a GBA slot cart made before DS slot carts were possible.
There are 4 types and aside from the EZ4 lite compact they feature NOR and RAM as well. Except this time the GBA code is stored on a ?SD card in the EZ4 rather than your DS slot card.
This ?SD can be miniSD in the case of the EZ4 original or microSD otherwise.
The EZ4 original and EZ4 lite (the latter being small enough to fit in the DS lite slot) have the same ram and NOR as the 3 in 1 above while the EZ4 lite deluxe has 48Mbytes of NOR and 32MBytes of RAM.
There is also a 2 in 1 tool from rudolph (he also does a 3 in 1 tool that a good deal of people use) that allows you to use the RAM of the EZ4 like you would use the RAM of the 3 in 1.
GBA games work on anything you can put the cart in (GBA, GBASP, GBM, DS, DSlite, Gamecube addon), no need for a passme. You only need a passme/nopass or to run flashme on your DS if you want to use the EZ4 to run DS code.
There are several third party tools (cory1492 does one called GBAldr, rudolph does one normally referred to as rudolphs 3 in 1 tool and Chuckstudios does one called ndstation) and some newer carts (cycloDS and acekard RPG are the two I know) even have the ability to use them for browser ram and rumble from the menu although I am not sure about their GBA support.