I think you need to think long and hard about why you want to go to your UG's law school. I decided to stay at my IU for law school. The decision to apply was based on the fact that I enjoyed Bloomington, understood the bureacracy, and I liked what I saw when I visited the law school. The decision to attend though was made because the law school had significantly more people and oppertunities in the industry I wanted to work in than other schools I applied to (and no, it's not the legal industry).
I would say there are lots of different opinions among adcomms about applicants from the undergraduate school on their university. I think one of the biggest issues is that there is a great chance of a yield protection waitlist, because an adcomm will look at your application as just applying to the school because you remembered it was there. I would do all optional essays to prove you really want to go there.
Note: all of this only applies to those applying straight out of UG. If you've been gone for even a year, it probably won't matter.
But think long and hard about why your are applying to your undergrad. I think a lot of people each year are trapped in law schools that aren't like their undergrad and become very disappointed. Also realize that going to your undergrad for law school is dangerous, since you are easily tempted to live and work like an undergrad. On the other hand, you have an intricate knowledge of a lot of things which create stress among your fellow students. You also have a built-in support structure outside of the law school which is essential during high stress times.