i use my slow cooker lots for all sorts of things. one thing i can't do is whole chicken - so no i wouldn't - it might end up raw in middle and dry on outside - and then you have wasted loads of food and nothing to eat - too risky
staine - easiest way to cook turkey is to lay 2 layers on foil on baking tray and then wrap it around turkey to form a tent - make sure there's no gaps, but room for steam to move around inside. it then steams itself and you just have to remove for last 30 mins and baste. make sure you dab a load of butter/marg on first.
if you want i can give you timings and oven temps. i always do it like this
6-10lb or 2.7-4.5kg is 20 min lb and 20 min over. if 10-18lb or 4.5kg-8.1kg allow 15 min per lb and 15 min over. preheat oven to 425/220c/gas 7 for first 40 mins and then turn heat to 325/170/mark 3 for remainder. remove foil for last 40 mins turn heat to 400/200/gas 6 and baste often.
it is so easy. just check there are no gaps in foil for steam to escape.