Before anything, I appreciate you sticking to the rule of three. It's just more satisfying.
Based on what I've seen, it seems like there isn't a native connector but that you should be able to use ODBC or Custom SQL to connect to Parquet files.
In that case, security is still likely going to be dependent on the database and the kind of connection you're capable of creating (I.e. sometimes people can only get an odbc connection to work without SSL on an SSL enabled database).
Have you tried to set up a connection?
Heya Jennifer -
This sounds like more of a data (Impala) question than a Tableau question. At the highest level, Tableau is happy when your data system (regarldess of what it is) answers questions quickly.
Parquet is certainly better than native CSV on HDFS. BUT, depending on the questions that you intend to ask, ORC might be better than Parquet.
There is no easy answer to this question because everyone's data is different. You'll probably need to experiment with this a little yourself to get a feel for how quickly Impala responds to the type of questions you ask.
I know this probably isn't exaclty the answer that you're looking for...but...it is what it is