Sorry I didn't quite understand the need to place a webserver between the (Android) application and Vertica. Does this mean the application talks to the webserver; the webserver retrieve data from Vertica?
Vertica supports a number of clients to connect to Vertica database such as JDBC, ODBC, etc. The Android application (or the webserver) would need to use one of these clients to connect and retrieve data from Vertica.
I would imagine that it is easier for your Android application to use JDBC (or ODBC) to retrieve data from Vertica than to connect to a webserver and have the websever queries Vertica.
Please let me know if this helped or you will need further clarification.