There is probably a upper limit, but practically you don't want more inodes than blocks. Since a non-empty file at least takes up one block, assuming that your files are all at least 1 byte, you couldn't use more inodes than blocks anyway.

(The exception are empty files, because on most filesystems an empty file does not use any data blocks, but possibly an inode to store file size, permissions, etc.)

If I'm not mistaken, some file systems store file contents smaller than a block directly inside the respective directory entry.