Does tolerance mean the same thing as indulgence?

They have similar meaning but are not exact equivalents.

"Liberal or lenient treatment" is both tolerance and indulgence.

However there are other meanings to both Words where this equivalence is not true. For instance

Tolerance also means a permissible deviation from a specified value of a structural dimension.

Indulgence also means something indulged in - eg fast sports cars.

As you can see these later two meanings could not be interchanged.