The only composite spoked wheels that are rated/approved/whathaveyou for tandems are the Aerospoke wheels. However, you could certainly contact the manufacturer of your other wheels and find out if they would have any issues with the wheels being used for a 350lb tandem team. I can anticipate what the answer might be, but you might just want to ask to "scratch that itch".
As for component wheelsets, properly-built, 36h wheels are more than adequate for your team weight. If fact, If you use a deep section rim you could probably even go with a 32h or 28h front wheel if you were so inclined.
There are, of course, a whole slew of paired, low-spoke count wheels now on the market for tandems. If you have a tandem with 160mm rear spacing Santana & Shimano have teamed up to offer what they call the "Sweet 16" wheelset which is based on Shimano's 1st generation paired-spoke wheel design. If you have 145mm rear spacing Bontrager offers a tandem version of it's RaceLite wheels and Rolf has released the Rolf Prima Vigor Tandem paired spoke wheel that is offered as an option or OEM wheelset on Burley and Co-Motion's go-fast tandems. These things retail in the $750 - $850 / pair range.