"indispensable to understanding" is correct and can be used in written English.
You could use it when you are emphasizing the importance of having a good understanding of something. For example: "The background knowledge of the subject is indispensable to understanding the material."
Discerning the ethnic and racial dimensions of politics is considered by some indispensable to understanding contemporary world politics.
Many original writers and thinkers — Martin Luther, John Adams, Samuel Taylor Coleridge — have filled their books with notes that are indispensable to understanding their thought.
Initially concerned with retarded development, Gesell came to the conclusion that an understanding of normal infant and child development was indispensable to understanding childhood abnormality.
Read Dominic Frisby's gripping Bitcoin, indispensable to understanding exactly what is occurring on the most important battlefield in the world — the battlefield of ideas.
Compelling and informative, "Fidel" is indispensable to understanding our Caribbean neighbor.
Phylogenetic relationships among basal hexapod lineages, the knowledge of which is indispensable to understanding hexapod origins and evolution, remain ambiguous despite numerous studies.
For example, the kind of theoretical maths that would terrify a layman has become an indispensable key to understanding the way that living things behave.
Written by Todd S. Purdum, a correspondent in the Washington bureau of The New York Times, and drawing together the work of dozens of his colleagues, "A Time of Our Choosing" is an indispensable guide to understanding the causes, conduct and consequences of the war in Iraq.
Purdum, a correspondent in the Washington bureau of The Times, deftly draws together his reporting -- and the work of dozens of his colleagues -- into what Michael Lind, writing in the Book Review, called "an indispensable guide to understanding the causes, conduct and consequences of the war in Iraq".
But they are indispensable to any understanding of what Mr. Michnik calls "the barren twilight" of totalitarianism in Eastern Europe.
