Their impact can both be positive, or negative. Being among the largest HODLers of Bitcoin, they should have the responsibility to help in the development of the Bitcoin economy, and in the aspect of Bitcoin education.
That is what scares me the most, if there are more companies that have a reserve in bitcoin will mean bigger prices because they will buy a lot of reserve as the company that they are. The good thing about this is that most cryptocurrencies will surely experience a price hike and many small hodlers will surely benefit from that.