I am mainly looking for answers from Roman Catholics and Eastern Catholics, although anyone is welcome to weigh in on this.
I would say no, since we are the True Church founded by Jesus Christ and the other Churches are in schism, that by financially supporting them we are financially perpetuating the sin of schism and, thus, are accomplices to this sin.
I think the Pope is getting ready to become Orthodox and this is just the first step at warming everyone up for his move. 
Well, given that any union will be a false union, and will foretell the coming of the Antichrist, as per a great many holy Elders..
..I'd not be wishing for this.
I suspect that I know what your answers to my questions aregoing to be, but I shall inquire anyway...
Scripture teaches us in the words of Our Lord, "That they all may be one; as thou, Father, [art] in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me." John 17. Given our Saviour's words, how can you rely on 'elders' in stating that ANY union will be a false union and a sign of the anti-Christ?
From the Litany of Supplication of the Liturgy of St. John Chrysostom: "Having prayed for the
unity of faith and the communion of the Holy Spirit, let us commend ourselves and one another, and our whole life to Christ our God.
Response: To You, O Lord."
Again, why bother with such a request, per your 'elders'? Isn't this therefore asking for something evil according to your statement? This petition is not translated as 'for the unity of THE faith" but rather for the 'unity of faith'?
I know you will dispute the meaning of both of these examples as I understand them, but I for one, will put my trust in the Bishops and teachers of the Orthodox Church rather than in some apocalyptic-prone 'elders.'
Per John 17, the KJV states: