There is only one kind of Hemlock - the Tsuga Canadensis, or Eastern Hemlock.  It prefers an acid, humous soil.  It might be a good idea to have your soil tested before purchasing a tree (http://soiltest.cfans.umn.edu/).  It also prefers a shadier location so it could do well in your yard.

Here is some additional information about this lovely tree:
http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=PGPIN06010

http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/choosing-landscape-evergreens/

Thanks Mary C.! The second link you sent , U of MN extension service, is where I got the name Canada hemlock...under evergreens  They must be one in the same..(?) Also, would white tail deer be a problem for this tree in the suburbs? We always have deer passing through. So sad this tree is having a rough time . I believe I have seen these at the Arboretum growing successfully, is that correct? Thanks again.

Yes, these names for this tree are the same.  I know it's a bit confusing but when all else fails you should look for the latin name of the plant that appears first (in this case it it Tsuga - a term that scientists have agreed upon how to differentiate some of the evergreen trees ).  After that name is a second term - the  sub-species (in this case it's Canadensis -  meaning it's origin is in the northern parts of our continent). Simply - plants are organized according to their genetic families (DNA) types, and then their sub-family types and then so on and so forth.

Deer....Well - the better the deer are doing, the worse our favorite plants do.
There are few, if any sure-fire ways to keep deer from browsing on our plants.
It seems that Hemlocks are not on the top of the list for deer, but if it's a hard winter, and/or there are no other choices deer will browse on anything.

If you are concerned about your new trees you should provide some protections for a few years.  After that the trees should be able to withstand a bit of "pruning: from the deer. http://virtual.clemson.edu/groups/psapublishing/pages/afw/afw6.pdf

Good luck with your tree choices!  thanks for contacting AaE