Yes, although as always it pays to be smart. Most turks have a very stereotypical view of homosexuals as wearing women's clothing and shouting. Moreover, Turks in general are more "touchy" than westerners, which means that casual touches from the same sex won't get too much of a reaction. However, kissing or other intimate gestures is probably best avoided in any of the more conservative areas, and might lead to a ton of unwanted propositions in the touristy zone. The best bet is to be discrete, as the police are unlikely to be sympathetic towards homosexuals, especially males. Again, a good resource for this issue is Istanbul-en.ihollaback.org or http://www.lambdaistanbul.org/ .