Many thanks for your enquiry concerning the pollination of tomatoes. If you're growing the crop now under heated glass and presumably some supplementary winter lighting then you will need to give the crop a helping hand but summer greenhouse-grown crops of tomatoes generally rely on insects.
Hand pollinating won't do any harm of course and you can always give the flowering trusses a gentle shake as you pass by; I recall from my days working in a commercial tomato nursery that early season crops where pollinate by a 'vibrating bee'; a rudimentary piece of battery operated equipment which had a quickly vibrating tip which was placed under the truss and sent clouds of pollen from the flowers! This was best done between 12 and 2pm as pollen travels fastest during the warmest part of the day and as it's unlikely you have a pollinating bee to hand, a light tap on the plant stem between flowering trusses will suffice.
I hope this helps; thanks again for your enquiry and good luck with your tomato crop.