The dimensional rift spawned from the crystal sample was controlled by Nihilanth, not Black Mesa. In fact, you try and close it in Half-Life when you launch the satellite, but it doesn't work since Nihilanth is keeping it open, and so Gordon has to kill Nihilanth.
Black Mesa did make easily manipulative portals before the Resonance Cascade, you see lots of them in the chapter Lambda Complex, there are whole puzzles involving them. And then of course the huge ass teleporter that takes you to Xen.
If you ignore the Displacer (I think it's stupid (not to mention not made by Valve), how would a device so little have the power to send you to Xen when it requires a giant reactor to keep the real Xen teleporter in lambda complex running?), Aperture Science could be credited with creating a mobile portal device, since all the portals in Black Mesa are stationary.