I also don't quite understand "dormant" if they have a balance.
However, yes all balances are totaled and then divided against your total Credit Limits to arrive at your percentage of utilization. However, even if your "overall" utilization is 30%, but you have certain cards at 50% or more, these will ding your score.
The balance/use things that affect your score are : percentage of utilization (amount debt in relation to credit limits), number of accounts with a balance, total dollar amount of debt.
Other things that affect your credit in this area is your payments. Not just if they are paid on time, but if you pay minimums only. Paying minimums only potentially flags that you are maxed out (income wise) and cannot handle more debt/credit.
So, 30% is not too terrible, but not good, especially when it represents around $10,000 in revolving debt. As the dollar amount increases, it can begin to outweight, as a factor, more so than percentage of utilization.