Answer
Yes, rental income can serve as proof of regular funds if it is documented as belonging to the applicant and continues to be received. This is not merely owning an apartment or house, but a rental income stream that can be documented through a lease agreement and payment records.
Proof of ownership, a valid lease agreement, bank records showing incoming payments, and tax documents, if applicable, are usually required. If the property is in Uruguay, a certificate from a local specialist may be required. For property abroad, plan ahead for document translation and legalization, as well as for the difference between gross rent and net income after expenses.
The weak point of this type of evidence is irregular payments or unclear ownership of the funds. One-off transfers from a tenant without a lease agreement look less convincing than a consistent payment history over several months. It is best to gather a set of documents that clearly shows who the owner and tenant are, how much is paid, and how long the agreement remains in force.