Let me add to Kent's comments and then provide some additional insights.
In the Nevada study that Kent mentions, if I'm remembering correctly the seeding failed, so the study could not conclude that the seeding was not impacted by grazing. In that particular study, we don't know the if there was an impact. Also, the grazing that occurred was not during the growing season, so that did reflect the what I saw in the literature. However, the literature is pretty scant on this topic.
Part of the "it depends" response is not just the site characteristics, but also the stocking rate and season of use.
If one is seeding sagebrush in the mid to late fall, then it is feasible that livestock might be used as a means of getting soil to seed contact, but there is no information on this approach. I can conceive of someone aerial seeding sagebrush in mid fall and then herding livestock across the seeding area to potentially trample seeds into the surface of the soil. If the soil is dry and the soil is fine textured then it might not work since the livestock hooves may not push the seed into the soil. If it is moist then it might work well, but one would need to make sure the it was not repeated for an extended period since that might create a compaction layer. If soils were coarser, then trampling might be effective and might not be as potentially detrimental.
During the first summer and into the following autumn after germination, but still during the establishment of the seedlings, I would suggest either no grazing or only very light use to allow seedlings to establish. Any seedling trampled during this phase is not likely to establish since the stems will be more fragile. Grazing use when it occurs should be light, not that there is a concern over sagebrush being eaten, but as use levels increase with more animals or more time on the site, the seedlings of sagebrush will be more likely to be trampled.
Should someone attempt to use this approach, it is extremely important that monitoring be done to document impacts if they occur. This might be a good MS study for a university student. If not, then be certain that an effective monitoring plan is in place, completed and reported so others can learn the results.
Regarding the second question, the key for enhancing sagebrush seeding success is to use equipment that will give sagebrush seed good seed-to-soil contact. The seed must be at or near the surface and using a packer wheel to enhance seed contact with the soil without getting the seed too deep is necessary to improve the probability of sagebrush establishment. Aerial seedings of sagebrush seem to show poor success if precipitation isn't above significantly above normal (20% greater than average). An aerial seeding with some soil disturbance may enhance success, but if a tractor is used to pull equipment that disturb the soil (e.g. harrow or chains), then why not seed directly on the surface and pack the seed. But even with the best seeding, weather in the year of the seeding (winter, spring and summer) plays the most important role in determining success. Success also depends whether there is significant competition from invasive annual grasses in the seeded area. If there is cheatgrass or medusahead in the area, then likelihood of success will be reduced. Annual grasses must be controlled if they are likely to be a problem. The fire may produce some control for the first year, but they will recovery quickly if they are at the site.
Others should feel free to comment on these suggestions.