B2G for small startups can work out if you can supply something that the government needs under a small business area. Look at SBIR (Small business innovation research) programs. The need for a network/capital depends entirely on the topic, and I think thats true regardless of B2B or B2G.
Sustaining B2G after the SBIR wins may or may not work out - its best if the area ties into some longer term need/consumable so you have some businesses with the gov't after the SBIR phase ends.