This is a much debated topic in mathematics for years.
To be frank value for zero raised to the power zero depends upon where you need it. Sometimes it is taken as 1 and sometimes as indeterminate (not infinity). Consider the following cases,
(1) In combinatorial or set theoretic approach zero raised to the power zero is equal to 1. This is because it represents some event that is not happening at all which is considered as a single event.
(2) In differential calculus and limit theory most of the time zero raised to the power zero is indeterminate.
Note: For GMAT purpose generally you'll never need this debated concept.
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