During the Shalosh Regalim when one is required to bring a shlomim as a korban chagigah there is also the commandment to rejoice.
I know that the matir for a korban is the zerikas hadam. If that alone is done is that enough or is it required to eat of the korban too? What then about a vegetarian or someone who is unable to eat meat (say for health reasons)?
As you wrote, the Matir of a Korban is the Zerikah. Once the Zerikah has been done, the owner attains the Kaparah as well. (See Rashi in Chulin 12a, who says that there is some Kaparah also in the eating; however, that element of the Korban is fulfilled at the Zerikah.)
On Yom Tov, however, there is an additional requirement of Simchah, and the Gemarah says "Ein Simchah Ela b'Basar," refering to Basar Kodesh, the meat of a Korban. It is because of this obligation that one who does not have other Basar Kodesh must bring a Shalmei Simchah. This Korban is only required for one who does not have other Basar Kodesh. If, for example, one had brought a Korban Todah, he need not bring a Shalmei Simchah. Here, regarding the obligation of Simchah, although the Korban does not require that the owner eat the Basar, the Yom tov requires that he eat it.
One who is unable to eat meat is an Ones just as in the case of any other Mitzvah. He is also not required to eat the Korban Pesach.
D. Zupnik