Yes, but it really depends on the nature of the trip and the details of the purpose. The U.S. does issue visas in the Spanish passports of Spanish citizens for a variety of reasons, not all of which involve an intent to reside in the US. Not all trips by visitors using a passport of a VWP country can use the VWP for admissibility to the US; and even if some such persons could use the VWP, some may not want to use the VWP.