Am I able to use a rail pass on these two train lines? I can't seem to find a straight answer on their website. Thanks!
Yes to both, but on both you will require buying mandatory reservations in addition to your passes.
Yes you can but watch out for the supplemental fees on the Thalys trains. For the Eurostar in Italy, the fee is about 10E. For the Thalys, it can be up to 60E for a 2nd class pass and up to 100E for a 1st class pass. Here's a link on the Eurail website that shows the supplemental fees. http://www.eurail.com/planning/train-seat-reservations/international-fees See the other message that is near yours on this same subject. There is an IC train that you can take in place of the Thalys train that your pass will cover completely but it takes an hour longer.