Can a stereospecific / stereoselective reaction produce a racemic mixture of enantiomers?
You haven't mixed up your terms: a stereoselective reaction is defined as one which preferentially forms one stereoisomer over another. Likewise, all stereospecific reactions are also stereoselective, also stereospecificity has stricter criteria then plain old stereoselectivity.

However, you have to remember that the term stereoisomer encapsulates both enantiomers and diastereomers. The hydroboration reaction is stereospecific because reacting one particular diastereomer of the alkene (either cis or trans) leads to one particular diastereomer of the product. It doesn't necessarily lead to a particular enantiomer. Basically, hydroboration leads to the formation of a racemic mixture of a particular diastereomer.

The alkene you have chosen, 2-methylbut-2-ene, is not a good example substrate that can actually show how the reaction is stereospecific. Since one of the alkene carbons is symmetrically substituted, there's no diastereomerism present in the products. If we use (2­E)-3-methylpent-2-ene as an example substrate, then it becomes clearer:



Note how neither of the (2​R,3​R) or the (2​S,3​S) stereoisomers are formed. However, the two products that are formed are enantiomers of each other.