In most cases yes. If your download is using up all the bandwidth you buy from your ISP then the game will get data loss as it attempt to compete for the limited bandwidth. Now if you set steam to limit its download rate so you have extra bandwidth left then your game should be ok. It will still be impacted by the download program competing for other resources in your computer like cpu,memory, disk etc etc. How much impact that has depends greatly on your machine and the game