Answer

No, in the usual Jain tradition, acharyas do not eat onions in any form, including dry onion or onion powder.

Explanation

Onion is considered a root vegetable, and root vegetables are avoided in Jain food discipline. This rule is followed even more strictly by Jain ascetics, including acharyas.

If you read a book saying otherwise, it may be:

• referring to a non-Jain context,
• using a different meaning of the word, or
• describing a practice that is not accepted in mainstream Jain monastic conduct.

Spiritual Understanding

Jain food discipline is based on non-violence and self-restraint. Avoiding root vegetables is part of reducing harm to living beings and maintaining purity of conduct.

Takeaway

For Jain acharyas, onions are normally not permitted. Strict Jain practice avoids them completely.