via an external AB it would be possible to call a webservice within a gen batch job.
You could access the web service via java, tcp/ip or Websphere MQ. It would most likely be a sync call via batch unless you are not interested in the result and just fire and forget.
.for TCP/IP you'd have to write customised code for the 'ezasoket' calls for the webservice for tcp/ip
.for java you'd have to write the customised calls to the APIs
.if you already have MQ at your site, you can see if they have a broker to facilitate an outbound call to your webservice.
You could call another eab first to generate the soap request via xml (customised code or xml composer?) and then pass this string into the eab that does the webservice call. makes it more component and resusable this way.
Just some ideas for you to investigate. I have worked at a site that utilised MQ as the transport for sending alerts via batch.