Can two different species in the same genus generally succeed in the same habitat?
It is not correct to say that genera are based on genetic similarity. Different lineages diverge genetically at highly variable rates, and there is no set cut-off for what defines a genus. Instead, genera are based on publications, which could be over 100 years old. Genera are not a biologically real category the way species are, so one genus may hold hundreds of species, while another, only one. Most of these genera were defined before molecular data was possible. There are no set phenotypic criteria for the definition of a genus, except that a well-described genus should have at least one fixed character that defines it. So in answer to your question, yes, two species in the same genus (congeners) will often exist in the same habitat. There would be selective pressures to separate them in terms of the niche that they occupy. The publication you referred to is simply a best guess: if you don't have information on the habitat requirements of a species, it would most likely share many similarities with its close relatives. Phylogeny is predictive, but different species in the same genus need not be identical in terms of their ecological requirements.