Acetals do not react with grignards. You can not have a nucleophilic addition on a multiple bond where there is no multiple bond, such as in acetals.
Furthermore, acetals can be used as solvents for the formation of grignard reagents and for their reactions (for example, methylal is a good solvent
for grignard reactions, see N. P. Cheremisinoff: Industrial Solvents Handbook, or similar reviews).