How can I generate a consistent entity graph (say from 10 tables) from a database fetch
Is it possible to do this in multiple queries but still realize the same level of consistency as having performed these individual selects as a single query?

It depends on the RDBMS.
In SQL Server you can use a transaction with SNAPSHOT transaction isolation level to get a consistent view of the database across multiple queries.
The isolation level Oracle calls SERIALIZABLE does the same thing.

My concern is one of performance of joining a large number of entities together in a single query

This is a valid concern because most RDBMS engines only return tabular results from queries. The strategies to generate a single tabular result for a complex object graph can lead to large resultsets and complex queries.  This has always been a problem for ORMs.