Big Data - Data Warehouse Solutions?
Can services such as AWS redshift or Google BigQuery allow you to
  somehow "import" data from many data sources and then you can perform
  SQL queries to join them?


It depends on your data and the type of joins you are performing. But, yeah, databases like Redshift can definitely perform better in your use case as they are column-based databases. Read this post and the associated answers for understanding how columnar data stores handle data.


  How about Hadoop and Hive?


Hadoop + Hive is mostly a DIY hosted/cloud version of what Redshift gives you on cloud.