IK Bones in Unreal and other skeleton questions

I see the default mannequin has IK bones in his skeleton, but it usually says only deform bones are imported into Unreal. Is that true? If IK bones/rigs are set up in an animation program is there no way to import them from the 3D app and use them in Unreal, or do you have to blue print IK on any imported skeleton?

Also I noticed that limb bones get sucked in - ie the upper arm is where the shoulder/clavicle should be, upper thighs are placed where pelvis bones would be but luckily it doesn’t appear to affect the weighting, but could cause issues with sockets etc. Is there a way to fix this or am I doing something wrong? I see the same thing is going on with the mannequins shoulder bones folding into an upper spine bone etc, but it gets me nervous as imported characters tend to get limbs sucked in a little more than the mannequin.