Yes, why not? If it's not something prohibited by the license, it is permitted. Also, if open source companies wouldn't do it, some open source projects would

Yes, why not? If it's not something prohibited by the license, it is permitted. Also, if open source companies wouldn't do it, some open source projects would never reach any kind of maturity if the company creating such project faces the competition who just live off the work of the original team who don't contribute back to the project.