I googled it up and found the scientific evidence I needed - "The Malaysian Stratigraphy (in Bahasa Malaysia) ". According to the papers, there're minor intrusions of limestone in Gunung Sumalayang. Photographs showing small stalactites and stalagmites on the cliff face backed up the findings.
Now, the big question is - are there any endemic snails living there? Since it's just a minor limestone intrusion and not the huge karsts like those in Central and Northern Peninsula Malaysia, it could have only supported a small population of endemic molluscs, if any at all. But, given the amazing diversity of microsnails discovered in just some tenths of metres of limestone in Sabah, it's worth exploring this potential site, right?Further Reading:
1.Norazhar Ngatimin and Teh G.H., 1993. Geology of the G. Sumalayang area, Johor. [abstract]. In: GSM Annual Geological Conference 93, Langkawi, Kedah, 12-13 June 1993, Warta Geologi 19(3):139.
2. STAG20022 Stratigrafi Malaysia: Stratigrafi Semenanjung Malaysia - Geologi Johor Timur, UKM.(link)
3.Menno Schilthuizen, Hsieh-Nee Chai and Tracey Elaine Kimsin,2003. Abundance and diversity of Land-snails (Mollusca: Goastropoda) on Limestone Hills of Borneo. The Raffles Bulletin of Zoology 2003 51(1):35-42. National University of Singapore. (link)