德瑞通票可不可以坐全程的冰川快线

不可以
If you have an InterRail or Eurail pass: InterRail & Eurail passes cover the Rhätische Bahn (RhB) between Disentis and Chur, but don't cover the Matterhorn Gotthard Bahn (MGB) between Zermatt & Disentis. So you'll need to buy a separate ticket for the Zermatt-Disentis part of the journey, as well as paying the Glacier Express supplement/reservation charge for the whole journey. The Zermatt-Disentis ticket costs about CHF 80 (£49), you can check this price at www.sbb.ch, just ask for the 2nd class fare from Zermatt to Disentis. Youth InterRail passes give a 50% reduction on this Zermatt-Disentis ticket, but with an adult pass you'll need to pay the no-reduction full fare. You can buy this at any Swiss station before you travel, along with your Glacier Express supplement/reservation.

含瑞士在内的Eurail通票在圣莫里茨-迪森蒂斯路段有效，但在迪森蒂斯-策马特路段无效。不过，Eurail通票持有人在购买此段行程的车票时可享受25%的折扣。乘客须另外付费提前预订车厢座位或餐车座位。
如果您想阅读更多关于这个信息, 我建议您查看：http://eurail.co/trains-glacier-express-qy

不能坐冰川快线列车，但是能坐同样线路的普通列车

似乎不能