How does Nature Shields Its Own work with "unblockable" and "can't be blocked"
Yes, the plant token blocks the creature even if that creature "can't be blocked". A ruling on Nature Shields Its Own's Gatherer page says


  The Plant token blocks the attacking creature even if the block couldn't legally be declared (for example, if the attacking creature has flying).


We can find other cards that do this by searching for the wording that Nature Shields Its Own uses: "onto the battlefield blocking". According to this magiccards.info search, there are 3 cards that do this: &#198;therplasm, Brimaz, King of Oreskos, and Flash Foliage.