Type Acceptance
Doesn't matter if you are a licensed ham or not. The radio is not type-accepted for use outside the amateur bands. This is not to say that it doesn't happen (does all the time, especially with the VX-150) but it is not legal.
With that said, if you do it, it's your responsibility to deal with any possible consequences. That's all I'm going to say about that.
As for a speaker mike, there is a public safety grade speaker mike available for the VX-150. It appears identical to the Vertex MH-45B4B, the only difference being the connector to the radio. Whereas the MH-45B4B has a large molded housing around the plug with holes for screws to secure the connector to the radio chassis, the mike that is available for the VX-150 simply has a plug. Sorry, don't know the model number, but you can most likely find it somewhere on the Vertex web site.
I'm not endorsing your usage of this radio on a public safety frequency. But you asked about a speaker mike. Yes, there is a good, high quality public safety grade speaker mike available from Vertex that would be great for amateur band usage.
EDIT: If you want a type-accepted radio for use on public safety VHF (with the licensee's approval) take a look at the VX-160 or if you want a display and more option buttons, the VX-180.