Posted By Chris Packham
My first question would be: "How probable is it that the mechanic will come into contact with the 'dirty' end of the vehicle and therefore be exposed to potentially contaminated soil?" If working on the engine end of the vehicle presumably this will be limited.
Secondly you may need to consider all three routes of body uptake (respiratory, skin and ingestion). Your risk assessment should show you what precautions you will need to take.
If you do provide gloves for the mechanics, these should be unlined (or flock lined) nitrile. The so-called "cotton lined" gloves are not generally suitable for chemical protection and natural rubber or PVC are not what I would recommend for work on an engine, due to the chemicals involved.
You will need to provide training in correct removal of gloves. Studies show that many people will contaminate their hands when removing gloves which largely negates the point of the gloves.
Finally, on skin care, avoid barrier creams as they provide little or no protection and can actually increase skin absorption. Also avoid anti-microbial cleansers (they can be counter-productive) but do provide an emollient lotion.

Chris