as we all agree ahmadis consider mirza ghulam a prophet so this excludes them from the circle of islam. namaz e janazah is offered for muslims.
Well I think what was being asked was do ahmadis have objections to ghair ahmadis participating in a funeral for a member of their community and not whether or not a muslim should participate in ahmadi funerals.
Not surprisingly the answer was yes they may. I suppose a muslim can also go to a christian funeral and sing a hymn or two and the christians would be more than happy to have him along.
As for brahmachari99 comment. Mirza Mahmood Ahmad had the right to call people who claimed to be Muslim a Kafir. According to the "Promised Son" Mirza Ghulam Ahmad the "prophet" was also involved in this business.
Personally I believe that it is a personal issue.
For example I think that both Mirza Mahmood Ahmad, and all Ahmadi Khalifas that followed him were not muslim. If Mirza Ghulam Ahmad held the same views as his son then I would personally not hesitate in calling him a non muslim.
However this is only my personal point of view.
If an Ahmadi wants to call himself a muslim then I will not stop him. However I will never personally accept him as a muslim.