Short answer. No. Article 1646 extends the buying disqualifications to leasing: persons who are forbidden to buy certain property are equally forbidden to become lessees of it. Because a guardian is among those barred from buying the property of the ward he protects, he likewise cannot lease that property.
What the law says
The persons disqualified to buy
Civil Code, Article 1646 — Who Cannot Be a Lessee. Read the full provision →
What the law says
are also disqualified to become lessees of the things mentioned therein
Civil Code, Article 1646 — Who Cannot Be a Lessee. Read the full provision →
The rule mirrors the ban on buying
The article works by cross-reference. It provides that The persons disqualified to buy under the Code's provisions on who may not purchase certain property are also disqualified to become lessees of the things mentioned therein. In other words, the Civil Code already lists categories of people forbidden, because of their position, from buying particular property — among them those who hold a relationship of trust or authority over the owner or the property. Article 1646 takes that existing list of buying disqualifications and applies it, unchanged, to leasing. Whoever cannot buy a given thing under those provisions cannot lease it either. The disqualification is carried across from one kind of contract to the other.
Why a guardian is caught by it
A guardian is squarely within the persons the Code disqualifies. The law forbids a guardian from acquiring the property of the minor or ward under his guardianship, because his duty is to manage that property faithfully for the ward's benefit, and letting him deal in it on his own account sets his self-interest against the very person he is bound to protect. Since a guardian cannot buy the ward's property, Article 1646 means he cannot become the lessee of it either. He is not permitted to turn his position of trust into a personal tenancy of the ward's land or things, taking their use for himself while charged with safeguarding them for another.
Why the same bar covers leasing, not just buying
Extending the ban from buying to leasing closes an obvious loophole. The reason a guardian is kept from buying the ward's property is the conflict of interest inherent in dealing for himself with property he controls for someone else. That conflict is just as present when he takes the property on lease: he would be fixing the rent, the term and the conditions of a contract in which he sits on both sides, as manager for the ward and as tenant for himself. If only sales were forbidden, the same abuse could be achieved through a long lease at a favourable rent. By disqualifying the person from leasing too, the article stops the prohibition from being evaded by choosing a lease instead of a sale.
What this means in practice
The practical consequence is that a person in a position of trust over property cannot lease it to himself, directly or through an arrangement that puts him on both sides. For a guardian, that means the ward's property is not his to rent; if it is to be leased at all, it must be to a genuine third party on terms that serve the ward, arranged with the proper authority and oversight that a guardian's dealings require. Anyone contracting a lease with a guardian, agent or similar fiduciary over the very property they administer should therefore pause, because a lease that runs foul of this disqualification is not something the law will uphold.