It is hard to say if going with a two person team is safe without knowing more about both climber's experience. Have they both had crevasse rescue training? Are they both absolutely proficient in it? How many glacier climbs have each completed? Which mountains? No mountains in Montana will replicate the conditions found on Rainier. In Washington only Mt Baker, Mt Hood, and the north side routes on Adams will give an idea of what to expect on Rainier. Do you trust your husband's life implicity with this other climber? Adding a third experienced partner to the team adds a large margin of safety. BC skiing really adds nothing to one's glacier travel and crevasse rescue experience, unless said skiing is done on glaciers.
Most runners/triathete types find climbing Rainier to be significantly harder than anything they have done previously, so their itinerary might be a bit optimistic. Their proposed itinerary concerns me for another reason. Their is no built in time to rest/rehydrate/acclimatize. If they start from the trailhead at 10-11 PM, they will not have any time to rest at high camp. Had they spent years climbing to altitude this may not be a problem; the body 'learns' and retains the ability to acclimatize. A more flexible itinerary would be to drive down Friday evening, spending the night at one of the higher campgrounds, (e.g. Cougar Rock or White River, depending upon the chosen route), start out first thing Saturday morning. This will allow a little
acclimatization. Hike to high camp Saturday morning, spend Saturday afternoon rehydrating and resting. Leave for the summit between 10-12 PM and descend the same day. The extra time spent at high camp resting and rehydrating will make a huge difference. This itinerary allows no time for acclimatization; climbers are essentially 'outrunning' altitude related illness which can work if one is fit enough. If they are pinned down high on the mountain, by a storm for example, serious complicatons can arise. It takes 5-7 days of yo-yoing to fully acclimatize to 14k. Of the altitude related deaths that have occured on Rainier, most have occurred when scientists or climbers spent the night on the summit without taking enough time to acclimatize.
My personal suggestion is hook up with a third, experienced climber; someone who has done Ranier multiple times as well as other big, glaciated peaks. This is probably going to be tough. Most experienced Rainier climbers want to climb hard routes, not the beginner ones. If they do decide to climb as a two person party they need to read up on two person glacier travel and practice building snow anchors, Z x C haul systems, prussiking, self arrest, etc. Andy Selters Glacier Travel book is an excellent resource. There are specfic tactics to improve safety for two person teams that work, but require training so in an emergency they can be employed without thought.
<shameless self promotion> http://www.summitpost.org/so-you-want-to-climb-mt-rainier/507227
This article includes some tips on climbing Mount Rainier, training tips, gear tips, as well as suggestions for helpful books, resources, and links to the NPS site for reserving camp sites and their permit system. </shameless self promotion>
Oh, my mountain climbing experience: I've been around the block a couple times.