Hello and thank you for your interest in Volcano World!
Volcano World has a page on Santa Ana @ http://volcano.oregonstate.edu/volcanoes/santaana/santa_ana.html that has information about historic eruptions and eruptive products.
While we have no information on the Ilamatepec name, a quick search brought up this paper about Santa Ana:
Sheets P D, 2004. Apocalypse then: social science approaches to volcanism, people, and cultures in the Zapotitan Valley, El Salvador. Rose W. I., Bommer J. J., Lopez D. L., Carr M. J., Major J. J. (eds), Natural Hazards in El Salvador. Bolder, Colorado, Geological Society of America Special Paper 375, pp 109-120.
I suspect it might have more information into the name and the cultures that named it. The GVP also has a great listing of alternative names and smaller sub-feature names that might help your research at http://www.volcano.si.edu/world/volcano.cfm?vnum=1403-02=&volpage=synsub
Santa Ana is monitored by Servicio Nacional de Estudios Territoriales (SNET) http://www.snet.gob.sv/ – You can find more information there too!
Visible Earth has an amazing satellite image of the 2005 eruption @ http://visibleearth.nasa.gov/view_rec.php?id=20315
I suggest a Google Scholar search on the terms – Ilamatepec history – I think I saw an answer there too.
Good luck with your research and thanks for a good question!