Curious, I have a couple virtually new Sebro brake rotors in good condition. I would guess they have a few thousand miles and other than missing the factory tool marks, they look new. Some small surface rust was cleaned up with a mild abrasive pad.

Do new brake pads need a certain microfinish on the rotors to "bed in" properly?

Street use only.

As long as you bed the pads, you are good.

To go a little further, I know a very good tech that likes older pads with new rotors or vs versa but his least preference is new with new. I remember using new pads with new rotors on one car that would barely come to a stop at the end of the driveway. I had to bed the pads a lot to get a good bite on the brakes.

Unless you are using EXACTLY the same pad compound old/new pads you should remove the transferred pad material layer on the rotors.

The best "finish" for pad bed in is an omni-directional finish.
This can be achieved by spinning the rotor while lightly holding a right angle dies grinder with a 3M scotch bright pad or a fine-grained sanding disc against each face. Sand lightly until fully swirled.

This is FREAKING easy on a rotor lathe. Takes less than 30 seconds after the final cut is done.

Fairly easy to do on the rear rotors. Bolt up to car, start engine, put in gear, and spin rotors.
Same shit with the die grinder.

Fronts will be a bitch. no good way to spin them at speed.

The very best finish is "Blanchard ground" but that's expensive (more expensive that new rotors usually).

In a pinch I have bead blasted to same effect.

Just hitting them with the die grinder (and rapidly rotate the grinder around the rotor) would probably work fine.

As they come out of the box there are radial tool marks as if cut with a lathe and are not smooth. After cleaning up, they are now smooth. Will this hinder the bedding?

The radial lathe marks are fine for organic pads.

Suck big donkey dicks for anything else.

When I'm cutting a rotor the last cut (after surface is clean) is done at the slowest feed speed and comes out almost mirror finish. On a decent brake lathe this can take 45 minutes.

After I get them that smooth, I hit them with the die grinder.

Now, if you're using real organic pads the finish should be rougher.

Organic pads are really hard to find nowadays. Almost everything is semi-metallic or ceramic and requires fine finishes.

Smooth is fine, still needs to be bare metal with no other pad material bonded to it, to allow the new pads to produce the transfer layer on the fresh faces.

This is the reason we "bed" pads and rotors in.

This info is for street cars, race cars often times swap between pads on the same set of rotors without finishing. Most of the time the owner will be swapping pads from the same manufacture with different characteristics.