It's quite common to get hops with seeds. As far as I know, they are not desirable for brewing but I wouldn't expect any serious off flavors unless your using copious amounts - 1 pound or more. At least, I've never heard anyone say that they are beneficial.
A little botanical lesson:
Hops are diecious- basically meaning that there are separate male and female plants. However, like many things in the natural world it's not a perfect rule and there are exceptions. Commonly you will find hermaphroditic plants where male flowers will sprout on a female plant or vice versa. Additionally, due to some genetic issues that occur from breeding some of the newer hop varieties, you can also find bisexual flowers. In this case the individual flowers have both stamens and pollen (the male parts) and pistils, carpels, and ovaries (the female parts).
In a large scale operation like where our hops come from, they can't possibly expect to remove all of these sexual anomallies and inevitably there is some pollination that occurs. It's also possible that wild hops from the area are pollinating the cultivated beer hops. Thus we get seeds in our hops.
Considering these facts, it's not surprising that some of the hops we get will have seeds in them. Certain varieties are more inclined to produce hermaphrodites and/or bisexual flowers than others - but I've no idea which ones. If it really bothers you though, you'll have to grow your own.
On a side note, I'm still trying to figure out if pollination causes a decrease in the lupulin production. Anyone who has any knowledge of hops' illegal cousin cannabis knows that pollination is detrimental to the production of those "desirable chemicals" in pot. The reason is that when a flower is pollinated, it puts all of it's energy into the production of the seed, not into the production of the chemicals, resins, and oils that it would otherwise. Seems to make sense that the same would be true for hops. This could be important because if pollination does reduce lupulin production, then a seedless hop and a pollinated hop are not going to give the same IBU's. If anyone knows more about this please reply or PM me (re: the hops, not cannabis