Given the choice, it must be better to have native trees for hosting epiphytes, vines and mistletoes because they are more likely to have complimentary life cycles. For example, a tawa host tree provides fairly consistent habitat conditions for an epiphytic species because it is evergreen and thus light levels and quantities of leaf litter are steady throughout the year. In contrast, the habitat conditions in a deciduous exotic host tree will vary with the seasons. This may not necessarily be detrimental to native epiphytic species but it is not conducive to the establishment of a natural community. I'll leave it there because I could ramble and speculate all day but I do think an exotic tree is better than no tree!
I'll leave you to contemplate the importance of exotic trees for epiphytes with a nice photo taken from a lovely gum :)