Many commercial vehicle insurers do not want to insure a driver with a commercial driver's license (CDL) that has a DUI, DWI or OUI. Since your last DWI was over six years ago, you might be able to find an insurance carrier that will insure you but the costs likely still be high.
I would check with the trucking school you are going to attend for more information since they typically would deal with the insurance companies that you would possibly want to be insured through. You can also find out if the school thinks you will be insurable through a company plan once you get a job after your truck driving school is over.
Our research found that companies hiring truck drivers varied about how far back a driving under the influence conviction had to be for a driver to be employed with them. This is probably due to the different insurance carriers' rules of who they will and will not insure. The information found includes: no DUI in the last 3 years and no more than 1 in the last 7 years, no DWI or DUI convictions within the past 5 years, and the driver will not be considered if convicted of a DUI, DWI or OUI due to alcohol within 4 years.
You can start a quote for commercial auto insurance here with us to see if any of our partners would find you insurable.