In my experience of doing such stuff, just don't go too extreme and you should be fine. What is your regular accent if you don't mind me asking? Mine is a very light midlands accent (English) but voice versatility usually stamps that out
:edit: after reading the thread I now understand you are asking generally and not for yourself :p
walk-in voice actors? Hah! Home studio for the win! :3
It will be a mixed bag of voices and it will be tough going in terms of finding the appropriate voices.
There are a few resources at our disposal in terms of advertising on professional game voice acting web sites that feature voice actors from the Call Of Duty series to newspaper advertisements if needed.
This will be our recording program in terms of side by side options:
a) Two studios will likely be recording on a set day: One in the UK and one in either Canberra or Sydney sometime beginning of next year. I can also book another studio I am comfortable with in Canada for individual recordings as I've dealt with them before and they have been pretty good and reliable and can FTP upload me the recorded files. I would only do this if there are enough voice actors in the area.
b) Some voice actors will have their own semi-professional recording setups at their home (one voice actor I am dealing with is in this particular category)
c) Others I may attempt field recordings with (likely with a Yeti Pro and MD-421 microphone plugged into a DR-680 provided I can update my recording equipment in time (costs a pretty a penny (likely need 700 AUS dollars before I can upgrade effectively) and I am doing so independently of FSE as a contractor).
d) In some cases people will be/have been auditioning for parts. Those that we feel don't need any supervision we will book into studios in their area (I will likely skype call them and sort out the particulars of the actual acting and get them to make some notes to take with them and will give them the voice list spreadsheet). The studio we book will need to have an engineer on site and be able to transfer recordings to us (or the individual who is doing the voice acting). This is something we did with 2 of the NW voice actors previously. This will be a likely option for extremely good U.S. based voice actors where we would be happy to go the extra mile to get professional recordings.
In any case I thought I would mention this since anyone is free to audition. If you want to audition then PM me and I'll send you my email address. The auditions won't require any professional recording equipment and I don't mind if the samples clip but I would expect you to record yourself yelling and acting out the following (in a similar style to NW voices):
Ready, Aim, Fire, Shoulder arms. (try to sound commanding as your shouting over enemy fire to be heard by men 10-30 meters away from you)
Don't shoot (surrender scared sounding)