If you are referring to the
resize_inode feature, then yes, you can resize a system created without this flag.
What this flag does, is to allocate much more space for file system inodes (that can't be change post filesystem creation). I don't remember the specific limits of growing a filesystem, but I think it was 1024 the original size for FS with
resize_inode and few dozen for FS without it.
Basically, online resizing of ext filesystems is dependent on the kernel, the amount of resizing possible, on available inodes.