Is there any API provided by Opentext for Opentext Content Server Pulse to interact with 3rd party clients as it was mentioned in Release Notes of Pulse.
Pulse mimics the twitterAPI for all of it's timeline functions so if you are looking to write your own app then the twitter API docs will get you up and running . ( http://apiwiki.twitter.com/ )
existing 3rd party twitter apps are a hit and miss since most of them are hard coded to connect to the twitter server. There are exceptions namely twirl, spaz and recently tweetdeck.
The only gotcha for these are authentication. You need to have your Content Server configured to use basic auth for these 3rd party apps to work with pulse.
Can I simply use a LAPI API to add a comment to a document through the pulse module?
No, Pulse is something new to CS 10 and LAPI 9.7.1 was the last release.
I have the Pulse Module installed on my Livelink 9.7.1. I understand that LAPI 9.7.1 is the last release, but is there a LAPI API to talk to pulse?
Unfortunately, no. Anything developed after the CS 10 release that provides an API will typically only offer a RESTful or SOAP interface.