The question I think you really asked was if the seams needed to be sealed or if the tent needed to be waterproofed before using.

As you've bought a $500 tent from REI, I wouldn't worry very much about waterproofing of the fabric. If you take it out back and test it with a hose, or if it leaks when you take it out camping (Rain is a good bet in PA in May/Jun) SEND IT BACK AND ASK FOR A REFUND. REI ought to grant that.

The other issue is the seams. Seams almost always leak. Until recently, the right answer was that you needed to seam seal (put a thinned-out glue) on the seams to prevent leaks, mostly through the holes for the stitching or through the seam itself. That's what Oregon Mouse was talking about with SilNylon tents. You use different products to seal the seams depending on what the manufacturer used to treat the fabric to make the fabric waterproof. The dominant waterproofing treatment for nylon tents - for years - was polyurethane. Cottage gear manufacturers often use silicon treated fabric. Mainstream manufacturers have been turning away from nylon for a while now in favor of fabrics that are waterproof by their very nature.

What changed recently is that large manufacturers have started taping seams to prevent leakage - an update I didn't understand when I bought my last family tent and spent a couple hours sealing every seam.

The REI website claims that your tent has been seam sealed. It doesn't say if the seams have been taped. If you open up the tent and look at the seams on the inside of the tent you will be able to tell if they've been taped because you'll see something that looks like a fabric tape on the back of every seam.

I recommend that you call REI (their customer service is OUTSTANDING) and ask what they think you should do. Ask to talk to an expert – they have them. You should ask what you should use to seam seal the tent, and if he/she would do so again if it were their family in the tent. Some tents are good out of the box, however (I was shocked when I used a Coleman tent out of the box and the seams were good to go) and if REI told me that their guys seamsealed the tent I just might trust that. Or you might find me out in the backyard sniffing glue to make sure that I wasn’t going to get wet. YMMV.