While tampering may or may not become an issue, bacterial contamination is a realistic concern...
While the studies were of dispensers in public restrooms, the contamination is thought to have occurred during the refill process, and biofilms are created.
"Refillable Soap Dispensers Are A Haven For Bacteria"
https://www.cleanlink.com/cp/article/Refillable-Soap-Dispensers-Are-A-Haven-For-Bacteria--22011
https://www.ncbi.nlm.nih.gov/pubmed/22257312
https://www.ncbi.nlm.nih.gov/pubmed/21421792
While the studies were of dispensers in public restrooms, the contamination is thought to have occurred during the refill process, and biofilms are created.
"Refillable Soap Dispensers Are A Haven For Bacteria"
https://www.cleanlink.com/cp/article/Refillable-Soap-Dispensers-Are-A-Haven-For-Bacteria--22011
https://www.ncbi.nlm.nih.gov/pubmed/22257312
https://www.ncbi.nlm.nih.gov/pubmed/21421792