I have used the notation $\vec{1}$ in a paper. I think that it's a good choice if you help the reader by defining it.  I did a Google Scholar such of "vector of all ones", and I found a lot of so-so notation such as $e$, $u$, $\mathbf{e}$, $\mathbf{1}$, and even just plain $1$.  I don't think that the literature is loyal to any particular choice.  Confusing $\vec{1}$ with a matrix would be a little strange, because a matrix is suggested by a two-headed arrow, or $\stackrel{\leftrightarrow}{1}$.