Pentaho does connect to Vertica ! just make sure you configure the drivers correctly ! As for the performance part ! Vertica will handle any query you have in less time then you think off !! I suggest you give it a try !! I connecting with Pentaho is hard or you cannot try Talend (open source ETL tool).
And for articles on how to install and manage your Vertica cluster follow this link . And for info on how pentaho connects do vertica check this link