The element <salute> is allowed to contain macro.phraseSeq. It is described as " a salutation or greeting prefixed to a foreword, dedicatory epistle, or other division of a text, or the salutation in the closing of a letter, preface". A very similar element <signed> ("contains the closing salutation, etc., appended to a foreword, dedicatory epistle, or other division of a text") is allowed macro.paraContent. The effect is that <list> is allowed in <signed> but not in <salute>.
The exemplar in front of me is from EEBO, TCP A88237 /STC E573_16. The attached graphic shows the original, and this is the (translated) TCP markup:
<head>Die Martis, <hi>1</hi> August <hi>1648.</hi>
<hi>Sir JOHN MAYNARD.</hi>
<hi>Sir PETER WENTVVORTH.</hi>
I believe the decision to encode that as a <list> is credible.