I think that you can have 'crossfading between layers' and dynamic crossfading between layers' (where the crossfading is controlled by velocity), but I am not sure what 'dynamic layers' are in this context. Do you mean that the layers are controlled by velocity? Because that is one of the ways that the layers can be defined... by velocity, so the layers are dynamic - by their very existence. Or do you mean that the samples within the layers are controlled dynamically - by a group for example?
If you mean 'dynamic crossfading between layers'? (which is where the velocity is used to continuously fade between one layer and another (where layers are defined by the samples allocated to ranges of velocities)), then Decent Sampler does dynamic 'switching' between layers, not cross-fading. Dynamic cross-fading is hard to create samples for, because during the cross-fade, both samples are playing, and so any pitch or phase differences become very obvious. This means that using synthesized samples is viable (with care in preparing the samples), but real-world samples of recorded instruments are very challenging because you can get audible phase cancellations with the slightest variation in the pitch of the instrument being recorded...