[ajxs]

It certainly is. The Korg Volca FM is implemented in this fashion, just to name one. From memory it uses an ARM Cortex-M chip for both the UI, and DSP. Many other modern synthesisers use COTS general purpose chips for DSP these days. At some point around the late 90s synths made the transition from being built around custom ASICs to using COTS DSP processor chips. It's hard to pin down exactly when this became standard. The Roland JP8000 (1996) used custom ASICs for signal processing, the Access Virus (1997) used a COTS DSP processor, from memory (Something from NXP?). The Korg MS2000 (2000) had a COTS DSP processor too. These days you can apparently achieve comparable performance with Cortex-M chips.