Vim has a large number of plugins available. There are plugins for almost everything: for different filetypes, color schemes, new commands or new features. Vem is compatible with most of them. The only plugins that may encounter an incompatibility are those that remap keys that are already mapped by Vem.
Most well written plugins take a lot of care to not to interfere with key mappings that the user may have defined. That's why most of them start their key mappings using the <leader> key (by default backslash \ both in Vim and Vem). If a plugin defines key mappings starting with <leader>, it should work in Vem as it does in Vim. However, some plugins don't follow this best practice. In those cases, they may override a key mapping set up by Vem and then, some Vem actions can make some actions to get altered or, directly, unreachable.
A word of caution
Once they realize the vast amount of plugins that are available, frequently new users find very tempting to start installing large amounts of them from the beginning. While plugins can be extremely useful, installing many of them indiscriminately can drag performance down, cause unexpected behavior of the editor and create cross-effects between mutually incompatible plugins.
It is usually a good idea to test any plugin that is installed to see if it is really useful and to see if it causes any problem. Also, when evaluating a plugin, consider that Vim may already offer a native solution to the problem that the plugin solves. Keeping a lean installation of the editor can help to keep it snappy and to avoid conflicts.