Is it true these are always fibrous? And that
they never pose a threat lifting pavers, seeking
cracked drains and crawling under foundations?
Peter

Yes the fibrous part of your question is certainly true, however some species can still make themselves pests, mainly entering drains/sewage via damaged areas ie cracks/joins etc I have often removed palm roots from piping that were longer than the palm itself.. fibrous or not they will still lift pavers and seek moisture where they are not wanted.