Offset says nothing about the rim clearance, unfortunately...
Of course the lower the ET the lower the chances of having clearance issues but that does not help. There are rims with the same offsetthat have 2cm of clearance, or 7mm of clearance or have negative clearance. So, my advice is: ET should not be taken into account. The best way is to measure the clearance (like I said above) to have an estimation...