There are not many strong links or similarities between The Fall of the House of Usher and The Oblong Box, but there are a few weaker ones. For instance, both are about the death of a woman, though that is by no means an uncommon subject in many of Poe's works. Also, both men (Roderick Usher and Mr. Wyatt) are noticeably changed by the loss of their loved one, which again is not uncommon. These two themes are often seen in Poe's works, whether together or not, so it is not a very strong commonality between the two.
However, there is one thing that is an interesting link: both men seemingly die with their loved one. I say "seemingly" because it is not clear whether or not either of them actually died, though it is strongly implied. Usher is fallen upon by his dead sister and is in his house when it collapses into the lake; Mr. Wyatt ties himself to his wife's coffin and jumps into the ocean, but does not resurface. Both were driven mad by grief, both were reunited with their loved one in the end.