Can documents used in settlement discussions be used as admission?

Unless and until they are a written documents towards settlement entered by both the parties, it may not be considered as evidence 

If there was negotiation through email excnaged bewteen the parties can very well be used an peice of evidance 

Electronic evidences are admissible in evidence  subject to compliance of sec  65b of Indian Evidence Act .

Thank you Adv. Kalaiselvan.  If the settlement did not take place, can the emails be used as admission? In other words, is willingness to pay in a settlement the same as admission of liability?

The settlement discussions over email cannot be enforced, even if you rely upon them during the trial proceedings, the court may not accept it as an evidence to decide the case in your favor because it is not a substantial evidence and there are no merits in such unreliable settlement discussions between parties.

The court will go by the case before it and cannot be influenced by such external factors until and unless they are substantial evidence to make some difference to your pleadings or the case itself.

Admission of a liablity through email is accepted in evidence when supported by a certificate u/s 65B IEA / 63 BSA 

What type of settlement you are referring to? Is it a Court monitored settlement through Mediation or through the Legal Services Authority leading to an Award?

All these are out of Court Evidence, and until the person or persons  making the settlement stands in the dock and testify the same and cross examined it can not go down as evidence, as it will be in the realm of hearsay evidence only.