Jamil says that pitching into wort, either the full batch of beer or even starter wort will kill roughly half the yeast. So, if you wanted to make a starter, rehydrate your yeast first.
The second point is, why make a starter with dry yeast?
When propagating yeast for pitching, the general rule of thumb is to increase the volume of yeast-to-wort by a multiple of 5-10x the current volume. There is enough yeast cells to ferment a normal gravity beer from one pack of yeast. Another rule of thumb is for every 30 pints of gravity you use another pack of yeast... So, 1.030 use one pack, 1.031-1.060 use 2 packs, etc. Making a starter with a pack of yeast does not really increase cell counts, and actually from reading the Yeast book, it can weaken the yeast cells due to depleted reserves. Your pitching a pack of yeast into a starter is like making a starter for a jar of yeast slurry. It's just not necessary. Your best bet is to make a small batch of beer, like 2-3 gallons of 1.040-50 OG, then use the slurry of that batch for about 10 gallons of beer, or split the slurry into 2 for 2 separate batches. I culture yeast from slants and this is what I do.
When people use Wyeasy Activator packs and make starters, it doesn't do much for cell counts (unless they are using a stir plate), but rather wakes the yeast up and gets them prepared to ferment. Propagator packs have significantly smaller amounts of yeast in them, and those are meant to be used in a starter. I believe it's the same rule of thumb with the White labs vials as with the dry yeast... For every 30 pts gravity you add another vital. But you can, and should make a starter with those.
As to using pint jars of slurry, I would never just take them out of the fridge and pitch them... You should take them out at the beginning of brew day so they come up to temperature. You want to pitch your yeast at as close to the wort temp as you can get so you don't shock your yeast.