While there certainly is some overlap, the investors in this round were venture capital most likely funded by institutional capital such as pension funds and endowments, rather than corporations who might be clients: see http://www.theequitykicker.com/2010/12/01/where-do-vcs-get-t... . And as of earlier this year they counted 450 unique customers: https://techcrunch.com/2017/04/05/snowflake-rakes-in-100-mil... So the extent of self-dealing is limited.

IMO, every company in every industry will need data warehousing at some point in their growth, if they are to survive in the modern world. It's difficult to get right, and Redshift is far from a white-glove experience for those attempting to navigate the space. Compared to B2C deals of this magnitude, this is significantly more sane.