You could have a bad balancing job on them or have a broken belt in your tire(s). You feel these problems in your seat for rear tires, and in your steering wheel for you front tires.
Alignment will not cause vibrations. I think uour putting wheels on car that was not designed for them. Contact the wheel manufacturer.
OE wheels are hub centric to your vehicle and often times custom wheels are not installed with a "hub centric ring" The only true wy to center the wheels on your Passat is from the hub not the lug bolts. Go back to the place you bought your wheels and tires and ask them if they installed hub centric rings on your car. They are a must on any FWD vehicle and 90% of the time fix the problem. Last option would be to contact a shop with a road force balancer.
I placed American Racing wheels on my new Toyota Van and ever since have had trouble with the front tires vibrating at about 50mph and above. I have had the wheels balanced about 5 tires and on the fifth time it was better but then 4 months later the vibrating returns. I am convinced that some after market wheels just are not made for certain vehicles.
I have a 2001 PT Cruiser. When the original tires became worn, I opted to take the original steel wheels off and put new aluminum wheels on the car. The first set of custom wheels were 16", low profile tires. I felt like I was literally tearing the road up with my steering wheel. I could feel vibration in my steering wheel at all speeds, but when I hit about 68 mph on the freeway, things got really rough. I thought maybe a tire out of balance, but when cruising at any speed between 68 and 75, it would be smooth, then my steering would go wild, then smooth, to infinity. The vibrations in my steering wheel would last maybe 5 to 6 seconds at a time, then smooth out. I thought it was just the low profile tires, so got another set of custom wheels and new tires in 15" but, I could still feel some of the vibration I felt with the previous custom wheels and new tires. My husband said I was just too darn picky and I thought maybe he was right. Until... I had the new 15" wheels & tires rotated. The vibration came back with a vengeance! The tire dealer checked for tires out of balance and checked to see if the front-end was out of whack. Nothing wrong. I asked, could it be the wheels? No, they said, because they put these wheels on other PT Cruisers and no one ever complained. After another week of grinding the road up, I took my old, original wheels and tires out of the shed and put them back on my car. What a difference! Smooth as glass. I am taking the car in next week to have them take the new tires off the custom wheels and put them on the old rims.
I had some 185/65/15's 88 spokes (which are for sale :-P) and the same thing has happened to me. I noticed if you get some build up of dirt on the inside of the rim it will cause for a rough ride. Clean the rims not just on the outside but on the inside and take her for a ride.
Does your steering shimmy side to side if so you need a toe adjustment. And go back to the dealer and see if they have the eccentric ring for your rims.
I also had after market wheels on my Toyota Sienna Van and then put new tires on them. The first thing I was told is that after market wheels do not always center on the hubs. The second problem is that not all new tires are perfectly round. The problem was solved by having the tires mounted on the after market wheels and then the tire shop put them onto a tire trueing machine that cuts the tread or maybe a better way of putting is that the tire and wheel are trued to a perfect concentric cirlce are that way matched. All vibration went away. It was like riding on glass!