Legally it technically is possible for the provider to give voice to voicebanks for both software.
However, Vocaloid voicebanks are not allowed to be transfered between the two softwares, so they can only be used with the software they are released for. You would not be allowed legally to use a Vocaloid voicebank for UTAU software, though could continue to use the UTAU voicebank in the software. So while the provider could provide for both, the voicebanks would always be only be able to be used for what they were made for.
Both UTAU and Vocaloid's licensing agreements do not support the transfer for voicebanks into each others software.
it has been done with the new vocaloid Macne Nana