You're talking about the Four-Thirds spec flash? All the Four-Thirds and Micro Four-Thirds bodies can use the same flash units. That's a standardized thing. There shouldn't be (read - shouldn't) any problems with it on the E-PL1, if it was made for the Four-Thirds standard.
If you're talking about the Vivitar flash spec'ed for another brand, then just use a single-contact trigger or sync.