Tagalog is descended from Spanish. Thus, if a Filipino cannot understand English, they should be able to understand Spanish at least well enough to get by.
First I would like to apologize for my somewhat angry response. I understand your frustration because I myself had a rather annoying experience with regards to being "Bilingual". I was having a job interview in San Diego and was asked if I was bilingual and I said yes. The interviewer started talking to me in Spanish to which I told her that no I don't speak Spanish but I do speak Filipino as my first language. She got irritated at that needless to say, I didn't get the job. Now, there is also a large population of Filipinos in San Diego area, not just Hispanics.
Now for correction, Tagalog is a regional dialect in the Philippines, not the national language which is Filipino. Filipino is a derived language which consists of Spanish, Chinese, Malay and Indian languages as well as Tagalog and other regional dialects.