Short answer. Yes. Rule 92, Section 2 of the Rules of Court expressly includes 'prodigals' in its definition of who counts as an incompetent for guardianship purposes, alongside civil interdictees, hospitalized lepers, and the deaf and dumb who cannot read or write — so reckless, wasteful spending on its own can support a guardianship petition even without any unsoundness of mind.
What the law says
the word "incompetent" includes persons suffering the penalty of civil interdiction or who are hospitalized lepers, prodigals, deaf and dumb who are unable to read and write, those who are of unsound mind, even though they have lucid intervals, and persons not being of unsound mind, but by reason of age, disease, weak mind, and other similar causes, cannot, without outside aid, take care of themselves and manage their property, becoming thereby an easy prey for deceit and exploitation.
Rule 92, Section 2 — Meaning of word "incompetent.". Read the full provision →
Prodigal is its own category of incompetent
Rule 92, Section 2 defines 'incompetent,' for guardianship purposes, as including several distinct categories, one of which is prodigals — people who habitually and recklessly waste their resources. This category stands apart from 'those who are of unsound mind,' which is listed separately in the same sentence. Because prodigality is named as its own ground, a relative does not need to show any mental illness or diminished sanity to be found an incompetent under this rule on account of reckless spending alone.
The other categories in the same definition
The same provision also treats as incompetent: persons suffering the penalty of civil interdiction, hospitalized lepers, the deaf and dumb who are unable to read and write, those of unsound mind even with lucid intervals, and — in a broader catch-all — persons who are not of unsound mind but who, because of age, disease, weak mind, or similar causes, cannot take care of themselves or manage their property without outside help and so become easy prey for deceit and exploitation. Prodigality sits alongside these as an independent, freestanding ground.
Why this rule still applies to an adult relative
Rule 92 originally governed guardianship generally, but the 2003 Rule on Guardianship of Minors now handles guardianship where the ward is a minor, leaving Rule 92 and the rest of Rules 92 to 97 to continue governing guardianship of incompetents who are not minors. Since a spendthrift relative is presumably an adult, this rule's definition of incompetent — prodigality included — is the current one that applies to their case.
What a guardianship petition still has to show
Falling within the definition of incompetent is the starting point, not the whole case — a guardianship petition still has to establish, on the specific facts, that the relative's reckless spending fits the prodigal category and that guardianship is the appropriate response. The rule does not itself set out that procedure or what evidence is needed; it only settles that being a prodigal, on its own, is a recognized ground for guardianship separate from any question of sanity.