Dan,
This depends on the acid profile of the grapes. Do you have any information about the malic acid level, for instance, in the grapes you plan on using? Do you know what grapes these are that you are getting from a vineyard?
Malic acid is tart - this is one of the reasons that some people introduce malolactic bacteria into their wines to help smooth this tartness out (this would otherwise be done over a long period of time, if I recall correctly). So if you use acid blend to increase the TA of your grape must, you will be increasing the malic acid levels. If your grapes are naturally high in malic acid, this may not be desireable. If your grapes are low in malic acid and you want the tartness or want to perform a malolactic fermentation, then it may be more desireable.
- Jim