It is possible but this method will take longer to grow the shrub and years to produce flowering. A much better and easier way of propagating lilac is through cuttings. This article will help:
In addition, lilacs are typically clump forming, producing new shoots from the base of the trunk. These shoots can be used for propagating lilac bushes as well. Dig down from the main clump, exposing the roots and cut the shoot away from the mother plant. Make sure you include roots. Then simply plant the shoot in a suitable location, watering regularly until it takes hold.