This is the summary I could get from an article in some other forum. (kept as a record for information)
"Order 37 CPC is best suited for cases in which a Defendant does not have a case at all and the Suit is prolonged for years. Also, cases in which loans are taken from Banks and borrowers disappear with no trace, Order 37 is useful as on the basis of loan documents, it is easier to get a decree from Court within a short time and then all that is left for a Bank to do is, to find the Defendant and get the decree executed. In fact, most borrowers, who otherwise are not scared of recovery agents, often offer settlement once they receive a summons and are reprimanded by the Courts."
This is the original query: "succession by imposter validity undrr 151 cpc"
The query lacks details and clarity.
However if the imposter gets such rights of succession through fraudulent means, this is fraud, and the only thing to be proved is that he is not such and such a person and legal heir and infact he is as per public records such person and declared his parents as such.
Definitely the simple issue is whether he is a legal heir or impostor and if the defendant files written statement, the plaintiff can certainly pray for such summary trial. (Very rarely court permitted disposal through summary findings)