Is there a name for a land mass that is an island during low tide but submerged during high tide?
I don’t think that’s quite it, Q.E.D.. A tidal island, as defined by your own link, is a piece of land that is connected to the mainland by a causeway that is exposed at low tide and submerged at high tide.
I think the term the OP is looking for is undesireable real estate. 
Years ago, on that kid’s gameshow version of Where In The World Is Carmen Sandiego?, they mentioned an island like this that was used as an airstrip. Twice a day, at the high tides, the island is under water. It might have been a military base. Whenever the island isn’t flooded, there are zillions of sea birds on it, and they have to send guys out to chase away the birds before planes can land.
Does “tombolo” fit your criteria?
That’s an isthmus that connects a rock or island to the mainland or to another rock or island and which is or may be covered by high tide and bared by low tide.
Ignatius
Local to San Francisco, one of the Farallon Islands (Middle Farallon, a.k.a. “The Pimple”) can be submerged at high tide and during large swells. We still call it an island.
Another example is the Albhros Rocks off the eastern coast of Brazil.
It looks like “rocks” “reef” or “island” all work for the geographic feature you’re looking for.
BTW, Diceman it almost sounds like you’re talking about [url=“http://en.wikipedia.org/wiki/Midway_Island”]Midway Island, because of the Navy’s problems with seabirds there, but I don’t think it’s submerged at low tide… could it be some part of the atoll?
The U.N. Convention on the Law of the Sea defines an island as “a naturally formed area of land surrounded by water, which is above water at high tide.”
What the OP describes is commonly known as a “rock”.
I’m no expert, but I concur with Danalan. AFAICT, an island is always above water, a shoal is always submerged, but anything that switches is a rock.
A rock??? LOL.
OK. 
I don’t think so. IIRC, it was a British posession.
I followed some links in the Wiki article, and it looks to me like a “rock” is a tiny island that’s basically just a big rock sticking up out of the water.
I think you’d call it a shoal or reef that dries at low water. See usage in that way on this page by none other than Capt. James Cook.
I believe that Princhester is correct. An island, in conventional usage, is land that is surrounded by water, but not submerged, at high tide. “Reef” or “shoal” is usually applied to land that is exposed or awash at low water, but submerged or awash at high tide. (However, sometimes “reef” may be applied to rocks that are near the surface but always submerged.) “Rock” has a variety of uses, and can apply to a very small island that is always exposed, a reef, or even a submerged feature near the surface. A “bank” is sometimes applied to land exposed at low water, and sometimes features below but near the surface.
Diceman, there’s an landing strip on Barra, one of the Hebridean Islands, which is submerged at high tide - longish but interesting article here, on the Scotland on Sunday site.
The island itself doesn’t get submerged…
Generally, a rock, but in order to complicate matters for the rest of humanity, politicians are conspiring to turn these things into something important.
If you sort the countries in the CIA world Factbook by are and look at the bottom entries, you will find the little-known French territory of Bassas da India.
I remember it because of the fantastic description it has been given, particularly the local landmark of Unnamed Location (alt. 2.4m).
Note that is is the subject of an international dispute, despite being a lump of rock in the middle of the ocean that is underwater at high tide. Cool, huh? It’s even more pathetic than the whole Denmark/Greenland argument over what is after all an actual piece of land.
Unfortunately there does not appear to be anything especially valuable near it, so we will probably be deprived of ‘La guerre de la Bassas De India’ or whatever.
You just need to market it properly. Play up the fact that it has access to a regular environmentally-friendly cleaning service.