Both Devil fruit powers have powers concerning the soul, with Brook's focusing on revival and -post timeskip- mastery of his own soul, and BM's focusing on control over the human soul in general. Which clearly would make for an interesting setup should one encounter the other.
One possibility would be that the Soru Soru no Mi is superior to the Yomi Yomi no mi in a similar way to the Magu Magu and Mera Mera no Mi, as it grants control over all human souls opposed to only the owner's soul. However, it's also possible that the greater control over one's own soul would be able to somehow counter the Soru Soru no Mi, and Brook has already demonstrated that, aside from manipulating the energy from his own soul, he's also capable of influencing other souls through his music, which shows he can already reach out to other souls in a way.
So, what are your thoughts? Will Big Mom be able to use Brook's unique condition to her advantage, or will he be the only straw hat immune to her powers? More importantly, will Brook organize a Homie music festival in the Seducing Woods?