dry erase is what you see on those big dry erase boards, like the one chad uses. wet erase is what you would see a teacher use with an overhead in class. both dry erase and wet erase can be used with a laminated sheet. the difference is that dry erase can be erase with fibers, while wet erase requires water, since it is water soluble. so dry erase are easier to clean, but i prefer wet erase because dry erase markers dry out quicker because they are alcohol based. also, dry erase markers tend to be much thicker than wet erase markers, so you have to write bigger. if you can request one or the other, i think wet erase is the way to go. you can write smaller and fit more on a page. you shouldn't have a problem with running out of sheets.
you should call your specific site to find out what their policy is. each site is different. here's what the ADA has to say about the current switch from dry erase to wet erase:
Previously two erasable note boards, two low-odor fine tip dry erase markers, and an eraser were provided to you by test center staff for your examination. However, sites are in the process of receiving new markers. These new markers are of better quality but they cannot be erased with an eraser. Therefore, sites will not be supplying you with an eraser. If you fill the two note boards and require additional note boards, please raise your hand and inform the test center administrator. The test center administrator will exchange one of your used note boards with a new note board. This change has not occurred at all sites yet but will be implemented within the next few months.