It’s possible to run Quicksilver and ServiceAPI on a same site, with some modifications, as I blogged here. However, if you go down that path, there is something you must keep in mind: They are not using the same authentication mechanism.
I’ve seen issues where Quicksilver implementations have some WebAPI controllers, which were working fine until ServiceAPI is installed. The controllers started returning null for CustomerContext.Current.CustomerContact, and so on, breaking some functionalities. It’s bad, yes, but it happens because of reasons.