Sharing in the Sacraments of the Eucharist, Penance, and Unction is of course permitted in particular circumstances in Canon Law; and and this is repeated in the Ecumenical Directory (with necessary distinctions between those communities which have valid sacraments and those which don't).
I recently did a post on the dangers of an ultratraditionalism which manufactures its own (often fierce) shibboleths upon a slight or even non-existent basis in the actual Tradition. An example of this problem (in addition to those I gave there) is the antipathy of some ultratraddies to the least whiff of anything savouring of Ecumenism ... especially communicatio in sacris between those in full communion with the See of Peter, and those not. They see this as another piece of post conciliar liberalism, and to be reprobated by Traditionalist Catholics.
This is why I welcome so warmly the admirable blog of the Transalpine Redemptorists which has recently published papal permissions from over the last seven centuries. I was not surprised to read the teaching of Pope Benedict XIV; that most erudite of Pontiffs knew his history too well to believe that the Auctoritas of the Tradition completely excludes such sharing. But I was particularly interested in the Toleration which Pius X signed for the Ukrainians in 1904; I was unaware of that. I could back up the evidence provided by the Redemptorists with accounts about how the authorities on both the Catholic and Orthodox sides positively encouraged all manner of sharing in the eighteenth century Aegean.
As soon as the Ordinariates have settled down, I hope consideration will be given to the question of how those provisions about this matter which are contained in the current Code of Canon Law should be used in the Ordinariates, so to enable them best to fulfil their role as effective ecumenical bridges which promote the restoration of full communion between separated Christians and the See of Peter.