Of course you can, unless the manual specifically says you shouldn’t. However, you should know that any flexible duct that is not completely pulled out adds to the friction, thereby dropping the effective CFM of your range hood a bit, while at the same time increasing the noise produced. So when possible, stay away from flexible ducting. For every 25 feet of ducting there is a 7% reduction in effective CFM when you use flexible ducting, where as it is 3% if you use non-flex ducting.