Yea, the issue with cement is the fact that it buffers the water to a higher pH. I had recently made a cement background for my African cichlid tank (
Here) and had to soak the water constantly with 4-5 total water changes till the pH equalized. Vinegar, since it is acidic, will hasten the loss of buffering capacity of the cement in your vivs, you'll just need to keep an eye on it. It probably is the most important part of the construction process.