Substituting vegetable oil spread for oil in cake mix
I have heard that you can. However, I would be reluctant to do so because rather than using 100% veg oil, you would be substituting a product that has only 53% veg oil. Most likely your end product would be drier.

Also, most veg oil speads contain salt, which could affect the flavor. And most contain water that could affect the texture. Depending on the specific product, various other ingredients may be present that could cause other issues.