Well, we do the simulations in Ansys, structures are exported in DXF, imported into Allegro.
Here you can either create a schematic symbol of the component (like a hybrid coupler, or filter) is created, so that the corresponding RF structure becomes a footprint with well defined connection points. Properties are added in the schematic (net_short) on the pins because unless you have the RF feature ($$$) Allegro has a hard time figuring out that a big blob of copper is a RF part, and not a short-circuit.
The advantage of that is that the RF structure can be easily manipulated like any other footprint.
You do need to keep track of units because DXF is terrible, if you import a metric structure as imperial, you're in trouble.
Allegro's RF feature I'm not familiar with. Apparently it lets you create all kinds of structures directly in the layout with parameters from Ansys.
Never tried it. My DXF/footprint approach works well enough for now. I've done many layouts like this with 5 to 6 structures per design.
Now for your other question, you can use whatever you want because the PCB software should be able to import a set of X,Y coordinates to draw the shape as a copper shape. It might not understand the purpose of the structure, and generate lots of errors, you just have to be careful.
Just pay attention to units and scale. Otherwise that Ka-band hybrid coupler you designed might only work at L band...
In many ways, you don't need much in terms of PCB software, except as a tool to create gerber files.