Henri Poincaré and Ernst Mach where physicists that worked in the same domains as Einstein. Mixing in the philosopher Hume make your citation very unprecise. Yet, even is debating about Hume had "significantly influenced Einstein's own subsequent ideas and beliefs", that does not mean it had an influence on his relativity theory.

Though I recon that Einstein philosophical and religious beliefs did influence his theory. IIRC, it lead him to alter his model of the universe so that it would be stable. After much criticism, he dropped the magic constant he had created for this.