Honestly, I don't know that Altium has evolved much since the Protel days, as far as basic SCH/PCB functionality goes. There's a lot of tiny savers, and a few bigger improvements. AFAIK, it's still pretty recognizable. (I haven't used anything earlier than AD09, so I don't know for sure how true this is.)
1. One example is: import whichever Gerbers you want, and set them to mechanical layers. I've done this for aligning components, board outlines, mechanical 3D bodies and such.
I wouldn't recommend doing this for an entire PCB design, but only a relevant selection of shapes or layers. Shit gets messy, fast.
2. Hmm, haven't tried this, but maybe build the net tie footprint on an inner layer (e.g., for a 4-layer board, enable Mid-Layer 1 and 2 in the library, and draw the copper and two pads on e.g. Mid-1). It should still track side just fine, and avoids the confusion (or impossibility) of trying to place a footprint on an inner layer. (Which by the way, is one of those small new features: around AD14 I think, they added support for components on inner layers, flipped or upright. This isn't madness, but is an unusual feature: the more advanced PCB houses can embed small passives inside the stackup... for added cost, of course.)
2a. Please, just... don't split planes. Bad example, maybe? But, yeah...
Tim