Can we use witnesses generated by OpenSSL's Rabin-Miller primality test to help factorization?
does that mean that OpenSSL has found a strong Rabin-Miller witness?


Yes, it does.


  if we could get OpenSSL to output the witness(es), how might that help us in the factorization of the value?


No, it wouldn't help; for most composite numbers, the vast majority of values are Rabin-Miller witnesses (it's provable that at least $\frac{3}{4}$ always are, but for most composites, the ratio is very close to 1).  By far the most frequent for the Rabin-Miller to claim compositeness is that the random value $x$ is a value for which $x^{n-1} \ne 1 \bmod n$ (and so you never hit a 1 or a -1 in the sequence); such a value $x$ proves that $n$ is not prime, but gives no indication of the factorization of $n$.  Now, if you found an $x$ for which you fail for the other reason; because Rabin-Miller hit a 1 without hitting a -1 first, such an $x$ would immediately yield a factorization.  However, such values of $x$ occur only extremely rarely in practice.