Glenn,

An attorney asked me this question a while ago and the analysis that I found was to the extent the beneficiary had a five and five power over the trust, the beneficiary was considered to own a portion of the trust and therefore some exclusion was possible.
In Revenue Ruling 85-45, old law, wife had a power of appointment over the QTIP and the exclusion was available. So you'll need to look at the document to see whether the surviving spouse has a power of appointment over the corpus and the extent of the power. See IRS Letter Ruling 200104005 and also PRL 200018021